A large fraction of the major unsaturated species (C2H2 C2H4, HCN, and HC3N) with mixing ratios of about 3 × 10−6, 10−7–10−8, 3 × 10−7, and 10−9–10−10 reside in Titan's atmosphere between 150 and 500 km (Vinatier et al., 2009; Coustenis et al., 2007) before they condense near the tropopause. A large flux of medium‐wavelength UV penetrates down to these levels, resulting in the polymerization of these unsaturated compounds and the formation of aerosols. We performed our experiments on aerosol formation at these altitudes where both abundances and solar UV flux are high, bearing in mind that additional photolysis occurs at both higher and lower altitudes. In the gas phase, C2H2 photolysis results in unsaturated C4 species that, on further addition of C2, form the cyclic benzene. These gas‐phase intermediates are consumed when an acetylene‐poor gas mixture is irradiated for a long time, giving rise to larger solid‐state species, mainly by addition of C2, followed by further cyclization. The largest species formed was the condensed 5‐ring benzpyrene, not the 7‐ring coronen molecule, which could have been detected there. Another fraction of the polymers consists of polyvinyl and vinyl acetylene chains, which are cross‐linked due to their labile π electrons and form an insoluble solid matrix. This explains the reduction of the C:H ratio from the condensed aromatics of 1.2 to the measured C:H = 1.013 ± 0.001 of the polymers.

Our model [Dimitrov, V., Bar-Nun, A., 1999. A model of energy dependent agglomeration of hydrocarbon aerosol particles and implication to Titan's aerosol. J. Aerosol. Sci. 30(1), 35–49] describes the experimentally found polymerization of C2H2 and HCN to form aerosol embryos, their growth and adherence to form various aerosols objects [Bar-Nun, A., Kleinfeld, I., Ganor, E., 1988. Shape and optical properties of aerosols formed by photolysis of C2H2, C2H4 and HCN. J. Geophys. Res. 93, 8383–8387]. These loose fractal objects describe well the findings of DISR on the Huygens probe [Tomasko, M.G., Bézard, B., Doose, L., Engel, S., Karkoschka, E., 2008. Measurements of methane absorption by the descent imager/spectral radiometer (DISR) during its descent through Titan's atmosphere. Planet. Space Sci., this issue, doi:10.1016/j.pss.2007]. These include (1) various regular objects of R=(0.035–0.064)×10−6m, as compared with DISR's 0.05×10−6m; (2) diverse low and high fractal structures composed of random combinations of various regular and irregular objects; (3) the number density of fractal particles is 6.9×106m−3 at Z=100km, as compared with DISR's finding of 5.0×106m−3 at Z=80km; (4) the number of structural units per higher fractals in the atmosphere at Z∼100km is (2400–2700), as compared with DISR's 3000, and their size being of R=(5.4–6.4)×10−6m will satisfy this value and (5) condensation of CH4 on the highly fractal structures could begin at the altitude where thin methane clouds were observed, filling somewhat the new open fractal structures.

The pp → ppϕ and quasi–free pn → dϕ reactions have been studied at the Cooler Synchrotron COSY–Jülich, using the internal beam and the ANKE facility. Total cross sections in the pp entrance channel have been determined at three excess energies ∊ in the range of 18.5–75.9 MeV. In case of the pn entrance channel the energy dependence of the cross section up to 80 MeV has been extracted by exploiting the intrinsic momentum of the neutron inside a deuterium target. Taken together with data for ω–production, a significant enhancement of the ϕ/ω ratio for both entrance channels of a factor 8 is found compared to predictions based on the Okubo–Zweig–Iizuka rule.

This is a presentation of a rigorous theory of fluidity of liquids, glass transition and melting of solids in the frame of an asymmetric double well potential model. Potential wells are doubled time to time by the local density fluctuations caused by the thermal longitudinal waves. The average frequency of doubling of potential wells is equal to the frequency of the most energetic waves which obey a law similar to Wein’s displacement law in black body radiation. Based on the equilibrium thermodynamic theory of fluctuations and the displacement law, a law of linear pre-diffusion mean-square displacement of particles in a solid is derived: the mean-square displacement of molecules within their potential wells increases linearly with temperature. It is shown that when this is broken-down (where the mean-square displacement at a certain temperature rapidly changes its slope as a function of temperature) glass devitrifies and crystal melts, and all possible solid–liquid transitions of a substance occur at the same critical mean-square displacement: any solid (not only crystals) transforms into liquid when the mean-square displacement, as a fraction of the average intermolecular distance, acquires a certain universal critical value – the same for different substances. It is proved that molecules in a liquid perform specific Brownian motion. The average jump distance is a function of temperature and it is much smaller than the nearest intermolecular distances. At a certain temperature, shown to be the Kauzmann temperature, the average jump distance of Brownian motion becomes equal to zero: the super-cooled liquid undergoes glass transition. The transition was proven to be a phase transition of the fourth order: the free energy of the system and its first, second and third derivatives are all continuous functions, but its fourth derivative with respect to temperature is discontinuous. Molecular mobility, diffusion and viscosity are obtained as functions of temperature.

We suggest that the methane observed on Mars can be formed by photolysis of water vapor in the presence of CO, in addition to possible geological sources, rather than biologically.

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

Received 22 June 2006DOI:https://doi.org/10.1103/PhysRevLett.97.029901©2006 American Physical Society

The pp->pp phi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the proton-proton final state interaction. Taken together with data for pp omega-production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

The liquid–glass transition is analyzed using a theory of Brownian motion in liquids recently developed by the author. It is shown that if a liquid could be cooled in quasi-static process and still avoids crystallization it would transform into a stable non-crystalline solid, which would be a normal thermodynamic phase. This hypothetical phase transition is neither first nor second order. At equilibrium transition temperature the free energy of the system and its first, second and third derivatives are all continuous functions, but its fourth derivative with respect to temperature is discontinuous. Therefore, the equilibrium liquid to non-crystalline solid transition may be considered a fourth order phase transition. The temperature of this phase transition, TK, which coincides approximately with the Kauzmann temperature, is below the standard glass transition temperature Tg. (When the temperature decreases below Tg, the viscosity increases above 1013dPas.) When the temperature decreases below TK, the system becomes an ideal solid because the molecular mobility becomes zero and the viscosity becomes infinite if we neglect vacancy-like mechanisms of mobility. This hypothetical quasi-static transition is physically unobservable because the real liquid–glass transition must be done at a cooling rate high enough to suppress the growth of nanocrystals, which makes the liquid–glass transformation a non-equilibrium complicated phenomenon. Understanding this ideal phase transition is a first step towards describing the real liquid–glass transition from first principles.

Glass transition has been one of the biggest challenges in condensed matter physics during the last century: in spite of significant progress we still cannot explain the sudden solidification of undercooled liquids on the atomic scale. The liquid state itself is one of the less developed branches of condensed matter physics. The theoretical concepts of atomic mobility, diffusion and viscosity in liquids are not in good agreement with experiments. In the present paper we attempt to answer this challenge by describing the thermal motion of the native molecules of the liquid as Brownian motion. On the basis of this theory we have derived general expressions for the atomic mobility, µ, self-diffusion, D, and viscosity, η for liquids. In dependence on a reduced temperature t, the mobility is expressed as µ = µ0m(t) for t ≥ 0 and µ = 0 for t ≤ 0 where µ0 is the mobility at the jamming point of the liquid, and m(t) is defined by t = m/(1 − e−m. The reduced temperature t = γ2T/γ c 2 Tc is determined by a quantity γ accounting for the anharmonicity of interparticle interactions in the liquid state. At the special values γc, and Tc, the mobility becomes zero, i.e. the equilibrium glass transition occurs when the reduced temperature becomes equal to 1.

We show that, the new experimental information reported by Saha et al. [Phys. Rev. C 70, 034313 (2004)] strongly supports the idea that the dipole band in $^{124}\mathrm{Xe}$ is a magnetic rotational band of intermediate nature, i.e., comparable amounts of angular momentum are generated by the shears mechanism and by the collective rotation.

Composite chiral bands, corresponding to the pi g(9/2)nu(h(11/2))(2) quasiparticle configuration, have been observed in Rh-103 and Rh-105. The behaviour of these bands is compared with that of the chiral bands with a pi g(9/2)nu h(11/2) quasiparticle configuration observed in the odd-odd Rh-102 and Rh-104 nuclei. This comparison shows in a model independent way that the energy separation pattern of the chiral partner bands depends strongly on the properties of the triaxial core whilst the dependence on the valence quasiparticle coupling and on the Fermi level is weaker.

Usually, the kinetic coefficient of crystal growth, i.e. the coefficient of proportionality of the crystal growth velocity to the undercooled temperature, is supposed to be a constant parameter. In the present study we show that this assumption is valid only for low undercooling temperatures, and in general it is a function of temperature. The kinetic coefficient was found to be a linear function of the temperature of the crystal/melt interface, which becomes zero for the glass transition temperature.

High-spin states in Rh-105 were populated by the Zr-96(C-13,p3n) reaction at beam energies of 51 and 58 MeV, and studied using the EUROBALL IV gamma-ray spectrometer and the DIAMANT charged particle array. A pair of nearly degenerate DeltaI = 1 three-quasiparticle bands with the same spins and parity have been observed. Comparison of the experimental results with tilted axis cranking calculations confirms the chiral character of the two bands, while arguments based on the excitation of particles within the pig(9/2)nu(h(11/2))(2) configuration of the yrast band and comparison with the previously observed gamma band exclude the other possible interpretations. This is the first experimental evidence for three-quasiparticle chiral structure in the A similar to 100 region, and the first simultaneous observation of a gamma band and chiral partner bands in one nucleus. (C) 2004 Elsevier B.V. All rights reserved.

A diffusion model of AlN layer formation by ion nitriding of Al is proposed based on the analysis of atomic transport during the process. This model is reduced to the following. Implantation of N ions to the surface of the specimen, named the reaction zone; extraction of Al from the substrate; diffusion transport of Al to the reaction zone through an AlN layer formed during the process; formation and growth of AlN in the reaction zone; sputtering of the AlN layer. Equations controlling the growth process have been obtained.

The Rh-105 nucleus has been studied with the Mo-100(B-11, alpha2ngamma) reaction at 43 MeV incident energy. A rich variety of structures was observed at high and low spins, using gamma-gamma-t and gamma-gamma-particle coincidences and directional correlation ratios. A gamma-vibrational band was observed for the first time in this nucleus. A new structure based on the intruder 1/2(+)[431] proton orbital was identified. Four magnetic dipole bands have also been observed at high spin, three of which have negative parity and have similar characteristics: they are very regular in energy spacing, presenting nearly constant alignments and large values of B(M1)/B(E2) ratios. Two of them are nearly degenerate in excitation energy and could be chiral partners. The pig(9/2)xnuh(11/2)(g(7/2),d(5/2)) configuration is tentatively assigned for these bands, with the angular momenta of the proton and neutron intruders and the collective angular momentum aligning along the three perpendicular axes of the triaxial core, as predicted by tilted axis cranking calculations.

Breakdown of the Einstein-Stokes relation in undercooled liquids is one of the unsolved problems in the theory of liquids. The self-diffusion coefficient follows the temperature dependence of the Einstein-Stokes equation D = kT / 6pietar at high temperatures but only down to approximately 1.2T(g) (T-g - glass-temperature). Below 1.2T(g) the temperature behavior of the diffusion coefficient is weaker than 1/eta. In the present study we show that this is a consequence of increasing correlations in the Brownian motion of the constituting particles of the liquid. We derive a relation, which includes the Einstein-Stokes equation as a limiting case for high temperatures.