Spectral-kinetic evidence of interaction of photochromic diarylethenes with silver nanoparticles

Spectral-kinetic investigations of the photochromism of some diarylethenes with sulfur-containing substituents in dimethylsulfoxide solutions with and without silver nanoparticles are performed. It is shown that silver nanoparticles chemically interact with diarylethene molecules, which is manifested in a change in the spectral and kinetic characteristics and photodegradation efficiency.     

Universal pion freeze-out in heavy-ion collisions

Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.     

Phase transitions characterized by polarization vector and rotation pseudovector in crystals of arbitrary point symmetry

A thermodynamic theory of phase transitions in crystals characterized by the rotational and polarization components has been developed. A list of phase transitions accompanied by the change of the group to a subgroup is compiled for crystals whose thermodynamic potential can be represented by a fourth-order polynomial with respect to the order-parameter components. Spontaneous polarization arising by the mechanism of improper phase transitions provided by the nonlinear relation between the polarization and rotational components is considered.     

Charged-particle multiplicity density at midrapidity in central Pb-Pb collisions at sqrt[S(NN)] = 2.76 TeV

The first measurement of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair √ S NN = 2.76 TeV is presented. For an event sample corresponding to the most central 5% of the hadronic cross section, the pseudorapidity density of primary charged particles at midrapidity is 1584 ± 4(stat) ± 76(syst), which corresponds to 8.3 ± 0.4(syst) per participating nucleon pair. This represents an increase of about a factor 1.9 relative to pp collisions at similar collision energies, and about a factor 2.2 to central Au-Au collisions at √ S NN = 2.76 TeV. This measurement provides the first experimental constraint for models of nucleus-nucleus collisions at LHC energies.