Role of the gas-liquid phase transition in the theory of nuclear matter

A sufficient condition for the two-nucleon interaction to produce a gaseous instability in the form of the appearance of inhomogeneous-spatial-density single-particle states of lower energy than the (homogeneous) plane-wave states is found to be simply that it gives binding in first order. The critical density at which the instability occurs thus signals the unambiguous breakdown of a plane-wave-based Hartree-Fock perturbation expansion for the ground state properties. Several examples are analysed.     

Strongly enhanced hole-phonon coupling in the metallic state of the dilute two-dimensional hole gas

We have studied the temperature dependent phonon emission rate P(T) of a strongly interacting (r(s) > or =22) dilute 2D GaAs hole system using a standard carrier heating technique. In the still poorly understood metallic state, we observe that P(T) changes from P(T) approximately T5 to P(T) approximately T7 above 100 mK, indicating a crossover from screened piezoelectric (PZ) coupling to screened deformation potential (DP) coupling for hole-phonon scattering. Quantitative comparison with theory shows that the long range PZ coupling between holes and phonons has the expected magnitude; however, in the metallic state, the short range DP coupling between holes and phonons is almost 20 times stronger than expected from theory. The density dependence of P(T) shows that it is easier to cool low-density 2D holes in GaAs than higher density 2D hole systems.     

Magnetically driven ferroelectric order in Ni3V2O8

We show that long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition in Ni3V2O8. The temperature and magnetic-field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry using Landau theory for continuous phase transitions, which shows that the spin structure alone can break spatial inversion symmetry leading to ferroelectric order. This phenomenological theory explains our experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.     

Synthesis and structure determination of bimetallic Au/Cu nanoparticles

The synthesis of bimetallic nanoparticles has become so important in recent times due to its multi-faceted applications. The structure of the synthesised particles influences directly their properties. In this paper, we report the synthesis of Au/Cu nanoparticles by a simultaneous reduction method, considering three different molar concentrations (AuCu, AuCu₃ and Au₃Cu) of the components. In order to determine the size and structure of the obtained clusters, the particles were examined by optical spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. One of the major factors, the minimum bimetal formation energy, was calculated by an embedded-atom method. The relation between the Au/Cu proportions has been demonstrated to affect the size of the particles and the corresponding structures. From the basic structural analysis it is found that the particles were fcc-like, multiple twin or multiple defect particles for the different Au/Cu concentrations. The smallest particles were identified for the Au/Cu sample with 50% of each, and the most crystalline structures were also obtained in the same sample. PACS 61.46.+w; 61.16.-d; 31.15.Qg     

Ferrocenyl-substituted α,β-unsaturated ketones in synthesis of tetrahydropyrimidinones

Ferrocenyltetrahydropyrimidin-2-ones were prepared by reactions of linear and cyclic ,-unsaturated ketones of the ferrocene series with urea in i-PrOH in the presence of t-BuOK. The structures of the compounds prepared were studied by ¹H and ¹³C NMR and IR spectroscopy, and also by single crystal X-ray diffraction.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1887–1893.Original Russian Text Copyright © 2004 by E. Klimova, Lorez, T. Klimova, Garcia, Hernandez, Ramirez.This revised version was published online in April 2005 with a corrected cover date.     

Entropy balance and evidence for local spin singlets in a Kagome-like magnet

We have measured the specific heat C(T) of the S = 3 / 2 Kagome-lattice-containing compound SrCr (9p)Ga (12-9p)O (19). We find little field dependence of the low-temperature C(T), consistent with a low-energy spectrum dominated by many-body singlet excitations. At high temperatures, we recover only approximately 50% of the total R ln4 entropy.     

Temporal cleaning of a high-energy fiber-based ultrafast laser using cross-polarized wave generation

We report the use of cross-polarized wave generation to perform both pulse shortening and temporal cleaning of a high-energy ytterbium-doped fiber-based femtosecond laser system. The nonlinear processes allow both a highly efficient nonlinear conversion of 20% and a large compression ratio of 3.5, with inherently improved coherent and incoherent contrasts. This results in the generation of 37 μJ, 115 fs pulses at a repetition rate of 100 kHz with high temporal quality.