High-density phases

Now, assume that the adsorbed layer is not a homogeneous phase but exhibits two-phase eoexistenee between the low density phase (1) and the high density phase (2) and that these two phases eontain Ni and N2 mole-eules, respeetively, and oeeupy the areas A j and A2. Of eourse, the total area of the sample is + 2 the total number of adsorbed partieles is... 

Two structural modifications are known for Me307F compounds (Me = Nb or Ta), namely low-density and high-density phases, Nb307F and aTa307F or PTa307F, respectively [192,248-250]. 

The value of the maximum mass of neutron stars obtained according to our analysis appears rather robust with respect to the uncertainties of the nuclear and the quark matter EOS. Therefore, the experimental observation of a very heavy (M > 1.6M ) neutron star, as claimed recently by some groups [41] (M ss 2.2 M ), if confirmed, would suggest that either serious problems are present for the current theoretical modelling of the high-density phase of nuclear matter, or that the assumptions about the phase transition between hadron and quark phase are substantially wrong. In both cases, one can expect a well defined hint on the high density nuclear matter EOS. 

The high-density phases of QCD at low temperatures can be realized in rotating compact stars - pulsars. Therefore, the observational data from pulsars could provide potentially important information on the state of matter at super-nuclear densities, in particular the superconducting quark matter. 

Since the discovery of the parton substructure of nucleons and its interpretation within the constituent quark model, much effort has been spent to explain the properties of these particles and the structure of high density phases of matter is under current experimental investigation in heavy-ion collisions [17]. While the diagnostics of a phase transition in experiments with heavy-ion beams faces the problems of strong non-equilibrium and finite size, the dense matter in a compact star forms a macroscopic system in thermal and chemical equilibrium for which effects signalling a phase transition shall be most pronounced [8],... 

The calculated critical lines for the binary pairs are shown in Figure 1. All these lines are discontinuous, indicating high density phase separations. For each binary pair the principal part of the critical line begins at the critical point for the component with the higher critical temperature. There is a second branch of each of the critical lines, beginning at the critical point of the component with the lower critical temperature, which terminates on intersecting a liquid-liquid-vapor three-phase line. 

The critical points in these mixtures are all at pressures higher than the critical pressure of water many are at temperatures higher than the water critical temperature. The mixture critical points indicate that high density phase separations persist to extreme conditions of temperature and pressure. 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

In order for the full coverage to be attained a relocation of molecules within the unit cell must occur. In the high density phase, even though the ads-ads interactions increase, the gas-solid interaction energy decreases owing to the stronger repulsion in the new equilibrium positions, giving a net repulsive decrease in the isosteric heat. 

Giovambattista N, Stanley HE, Sciortino E. Relation between the 61. high density phase and the very-high density phase of amorphous... 

It seems that the method to fix the size parameter of the Leonard-Jones potential to match the density of ambient water is unable to predict the internal energy of the high density phases of ice. 

It is well known that irradiation alters the structure of ice. It is amorphized at T < 80 K by protons, ions, photons and electrons. The structures of the irradiated ices have only been determined in the case of intense electron irradiation, where the high-density amorph was detected. Recent molecular dynamic simulations have also shown a densification of the ASW ice when irradiated with 35 eV water molecules,but these simulations also questioned the existence of the high-density phase as the initial structure of ice films deposited at low temperature. 

Narten et al. also deduced from their data that one fifth of the water molecules are located at this additional distance. In a RDF picture, this corresponds to 4 nearest-neighbours at 2.76 A and 1 second neighbour at 3.3 A. This matches well the atomic surrounding depicted by the cluster corresponding to the structure of ice after the irradiation (cluster 2). The local order before the irradiation is better described by the 4-coordinated tetrahedron found in the normal amorphous low-density ice and in the crystalline ice (cluster 1). Thus we conclude that the structure of the ice film before the irradiation is not that of the high-density phase but that of the normal low-density phase. In addition, since the irradiated ice has a local order similar to what expected in the high-density phase, we also conclude that the photolysis at 20 K has induced the phase transition from the low-density to the high-density amorph. 

Giovambattista N., Stanley H., Sciortino F. (2005) Relation between the High Density Phase and the Very-High Density Phase of Amorphous Solid Water, T /2j5. Rev. Lett. 94(10), 107803-107807. 

Wurlitzer A, Politsch E, Huebner S, Krueger P, Weygand M, Kjaer K, Hommes P, Nuyken O, Cevc G, Loesche M (2001) Conformation of polymer brushes at aqueous surfaces determined with X-ray and neutron reflectometry. 2. High-density phase transition of lipopolyoxazolines. Macromolecules 34 1334-1342... 

HD High Density phase with high carbon content, ca. 20 % C, stable... 

Figure 7.6 (a) Compact aggregate in equilibrium with a dilute colloidal dispersion. As time evolves, the aggregate grows and in equilibrium, there is macroscopic phase separation between the iow- and high-density phases, (b) Schematic representation of a fractai aggregate. 

Recently, Mahecha-Botero and co-workers presented a generalized comprehensive model which characterizes multiple phases and regions (low-density phase, high-density phase, staged membranes, freeboard region) with the possibility to include new features or simplifications in order to simulate different fluidized bed (membrane) reactors. For a more detailed description of the model and assumptions an interested reader is referred to. ... 

Description of the properties of matter is punctuated by phase transitions. While formally such transitions can occur only in the (extensive) matter limit, the manifestations of a matter phase transition in a finite system can profoundly affect the behavior of a finite clump of matter. In nuclear science, symmetric matter must undergo a hquid-to-gas-like transition as the matter is heated and the average density reduced, since it has an attractive interaction that can be saturated at short-range. Just as in the case of standard fluids, there will be a coexistence region that self-partitions into low- and high-density phases. Just how this transition is manifest in real charged and finite nuclear (i.e., in the real nonextensive) systems has been the focus of considerable effort. 

Desgreniers S (1998) High-density phases of ZnO structural and compressive parameters. Phys RevB58 14102-1405... 

For nonzero temperatures, the model phase diagram given in terms of the reduced chemical potential, Jl = p/e, versus reduced temperature, T = k T/e, is illustrated in Fig. 6. Data are from numerical simulations for y = —2e. As the temperature is increased the low- and high-density phases that may be identified as amorphous, due to a zero diffusion coefficient, smoothly turn into low- and high-density liquids, respectively, analogously to the two-dimensional case. 

A feature that distinguishes the Bell-Lavis model from the ALG models discussed in the previous section is that even the lowest energy configurations of the high-density phase (p = 1) involve frustration of the hydrogen bonds. As a consequence, the LD phase is present also for attractive van der Waals e < 0, in contrast with both versions of the ALG. 

The alkali metals are of major scientific and technological interest. For this reason, a great deal of research effort has been devoted to their physical properties, despite severe experimental difficulties associated with their high chemical reactivity. Some of the current and potential applications of fluid alkali metals are mentioned in Section 1.3. From the perspective of fundamental science, the alkali metals occupy a special place. In their normal (high density) phases, they are among the simplest of metals their electronic structure and properties more closely approximate those of the free electron gas than any other elemental group. 

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