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81.
We consider a three-dimensional lattice model of a network-forming fluid, which has been recently investigated by Girardi et al. by means of Monte Carlo simulations [J. Chem. Phys. 126, 064503 (2007)], with the aim of describing water anomalies. We develop an approximate semianalytical calculation, based on a cluster-variation technique, which turns out to reproduce almost quantitatively different thermodynamic properties and phase transitions determined by the Monte Carlo method. Nevertheless, our calculation points out the existence of two different phases characterized by long-range orientational order, and of critical transitions between them and to a high-temperature orientationally disordered phase. Also, the existence of such critical lines allows us to explain certain "kinks" in the isotherms and isobars determined by the Monte Carlo analysis. The picture of the phase diagram becomes much more complex and richer, though unfortunately less suitable to describe real water. 相似文献
82.
Costa D Ruberto R Sciortino F Abramo MC Caccamo C 《The journal of physical chemistry. B》2007,111(36):10759-10764
We report a study of the mode-coupling theory (MCT) glass transition line for the Girifalco model of C60 fullerene. The equilibrium static structure factor of the model, the only required input for the MCT calculations, is provided by molecular dynamics simulations. The glass transition line develops inside the metastable liquid-solid coexistence region and extends down in temperature, terminating on the liquid side of the metastable portion of the liquid-vapor binodal. The vitrification locus does not show re-entrant behavior. A comparison with previous computer simulation estimates of the location of the glass line suggests that the theory accurately reproduces the shape of the arrest line in the density-temperature plane. The theoretical HNC and MHNC structure factors (and consequently the corresponding MCT glass line) compare well with the numerical counterpart. Our results confirm the conclusion drawn in previous works about the existence of a glassy phase for the fullerene model at issue. 相似文献
83.
Gambi CM Giordano R Chittofrati A Pieri R Laurati M Baglioni P Teixeira J 《The journal of physical chemistry. B》2007,111(6):1348-1353
Aqueous mixed micellar solutions of perfluoropolyether carboxylic salts with ammonium counterions have been studied by small-angle neutron scattering. Two surfactants differing in the tail length were mixed in proportions n2/n3 = 60/40 w/w, where n2 and n3 are the surfactants with two and three perfluoroisopropoxy units in the tail, respectively. The tails are chlorine-terminated. The mixed micellar solutions, in the concentration range 0.1-0.2 M and thermal interval 20-40 degrees C, show structural characteristics of the interfacial shell that are very similar to ammonium n2 micellar solutions previously investigated; thus, the physics of the interfacial region is dominated by the polar head and counterion. The shape and dimensions of the micelles are influenced by the presence of the n3 surfactant, whose chain length in the micelle is 2 A longer than that of the n2 surfactant. The n3 surfactant favors the ellipsoidal shape in the concentration range 0.1-0.2 M with a 1/2 ionization degree of n2 micelles. The very low surface charge of the mixed micelles is attributed to the increase in hydrophobic interactions between the surfactant tails, due to the longer n3 surfactant molecules in micelles. The closer packing of the tails decreases the micellar curvature and the repulsions between the polar heads, by surface charge neutralization of counterions migrating from the Gouy-Chapman diffuse layer, leading to micellar growth in ellipsoids with greater axial ratios. 相似文献
84.
G. F. Cerofolini A. Giussani F. Carone Fabiani A. Modelli D. Mascolo D. Ruggiero D. Narducci E. Romano 《Surface and interface analysis : SIA》2007,39(10):836-844
A combined analysis, based on angle‐resolved X‐ray photoelectron spectroscopy and multiple‐internal‐reflection infrared spectroscopy, of the (1 0 0) silicon surface after etching in dilute aqueous solution of HF is presented. The analysis shows that the surface is mainly formed by a heterogeneous distribution of SiH, SiH2 and SiH3 terminations, but contains (in addition to sub‐stoichiometric oxidized silicon) a form of reduced silicon, not consistent with the currently accepted picture of the native HFaq‐etched surface. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
85.
P.?SwiderekEmail author 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,35(2):355-361
The effect of electron exposure at an incident energy of 10.5 eV on solid
molecular multilayer films containing nitromethane-D3 has been studied
by high-resolution electron-energy-loss (HREEL) spectroscopy.
Nitromethane-D3 was mixed with varying amounts of hexane or heptane to
investigate whether the hydrocarbon component or, more specifically,
resonant H- production which is known to occur at electron energies
around 10 eV plays a role in electron-induced modifications of the nitro
group. While bands related to vibrations of the nitro group clearly diminish
under exposure, the rate of this process does not depend on the amount of
the admixed hydrocarbon component. Consequently, the hydrocarbon component
and thus also the H- producing resonance around 10 eV do not determine
the rate of modification of nitromethane-D3 at the investigated energy. 相似文献
86.
87.
R. Lo Franco G. Compagno A. Messina A. Napoli 《The European physical journal. Special topics》2008,160(1):247-257
We show that the N-photon generalized binomial states of electromagnetic field may be put in a bijective mapping with the
coherent atomic states of N two-level atoms. We exploit this correspondence to simply obtain both known and new properties
of the N-photon generalized binomial states. In particular, an over-complete basis of these binomial states and an orthonormal
basis are obtained. Finally, the squeezing properties of generalized binomial state are analyzed. 相似文献
88.
We consider density matrices which are sums of projectors on states spanning irreducible representations of the permutation
group of L sites (eigenstates of permutational invariant quantum system with L sites) and construct reduced density matrix ρ
n
for blocks of size n<L by tracing out L−n sites, viewed as environment. Explicit analytic expressions of the elements of ρ
n
are given in the natural basis and the corresponding spectrum of the reduced density matrix is derived. Results apply to
other quantum many-body systems with permutational symmetry. 相似文献
89.
Castrillo A Casa G Palmieri A Gianfrani L 《Isotopes in environmental and health studies》2006,42(1):47-56
The potential use of high sensitivity laser absorption spectroscopy for measuring the 13C/12C isotope ratio in atmospheric CO2 has been demonstrated, using a GaSb-based diode laser at 2.05 microm. In this spectral region, the overlapping between relatively strong 12CO2 and 13CO2 absorption features gives rise to several line pairs which are well suitable for a spectroscopic determination of the isotope ratio. Preliminary results have demonstrated that a short-term precision better than 1 per thousand can be easily obtained, for a CO2 concentration of 1000 ppm. We extensively discuss the influence of a possible non-linearity in the detectors' response on the delta-value and suggest an instrumental development that would allow to eliminate this effect. 相似文献
90.
《Physica A》2001,289(1-2):278-289
In order to establish effective detoxification plan, it is necessary to analyze and understand the nature of radioactive contamination. This process is hindered by the highly complex mechanism, responsible for the interaction between different radionuclides with each other, subsequent cumulative effects, and influence of climatic and geological processes on the diffusion of contamination through soil, water and air. The complexity involved in modelling such an environment requires the use of novel, more flexible and powerful techniques. We have found that the application of stochastic geometry enables us to distinguish between naturally occuring and man-made radionuclides. 相似文献