An investigation of the SCOZA for narrow square-well potentials and in the sticky limit

We present a study of the self consistent Ornstein-Zernike approximation (SCOZA) for square-well (SW) potentials of narrow width delta. The main purpose of this investigation is to elucidate whether in the limit delta --> 0, the SCOZA predicts a finite value for the second virial coefficient at the critical temperature B2(Tc), and whether this theory can lead to an improvement of the approximate Percus-Yevick solution of the sticky hard-sphere (SHS) model due to Baxter [R. J. Baxter, J. Chem. Phys. 49, 2770 (1968)]. For SW of non vanishing delta, the difficulties due to the influence of the boundary condition at high density already encountered in an earlier investigation [E. Schoell-Paschinger, A. L. Benavides, and R. Castaneda-Priego, J. Chem. Phys. 123, 234513 (2005)] prevented us from obtaining reliable results for delta < 0.1. In the sticky limit this difficulty can be circumvented, but then the SCOZA fails to predict a liquid-vapor transition. The picture that emerges from this study is that for delta --> 0, the SCOZA does not fulfill the expected prediction of a constant B2(Tc) [M. G. Noro and D. Frenkel, J. Chem. Phys. 113, 2941 (2000)], and that for thermodynamic consistency to be usefully exploited in this regime, one should probably go beyond the Ornstein-Zernike ansatz.Comment: 40 pages, 13 figures. Previous Sec. 2 on the Yukawa potential has been removed. Only the square-well potential is considered in this versio

Different characteristics of triptans

Despite the pharmacokinetic differences among triptans and the variety of ways of administration, the clinical differences in everyday use of these drugs do not allow a largely accepted decisional tree. There are a number of comparative trials showing similar results with regard to efficacy, safety, and tolerability of these drugs. This means that the patientrsquos preference is one of the most important decisive factors in choosing one triptan over another. A good migraine therapy requires a balance between patient satisfaction and drug efficacy and safety. All the marked triptans show a good benefit-risk ratio, and comorbidity should be considered when choosing between different triptans

Differential involvement of central 5-HT1B and 5-HT3 receptor subtypes in the antinociceptive effect of paracetamol

Objective: We investigated the effect of pre-treatment with ondansetron or CP 93129 (a 5-HT1B agonist) on the antinociceptive activity of paracetamol and the changes in central 5-HT3 receptors induced by paracetamol alone or co-administered with ondansetron. Materials and Subjects: Male Wistar rats (eight per group) were injected with ondansetron (2 and 4 mg/kg s. c.) or CP 93 129 (0.5, 1 and 2 mg/kg s. c.) 15 min before paracetamol (400 mg/kg, i.p.). Methods: Pain threshold was evaluated in the hot-plate or in the paw pressure test 30 min after the last treatment. 5-HT3 receptor binding capacity was measured in the frontal cortex, temporal-parietal cortex and midbrain by means of radioligand binding technique. Statistical analysis was done using ANOVA followed by Student-Newman-Keuls test and 2 X 2 factorial analysis when appropriate. Results: Pre-treatment with ondansetron, at doses of 2 and 4 mg/kg, did not affect the antinociceptive activity of paracetamol in the hot-plate test and in the paw pressure test. Paracetamol did not change the characteristics of 5-HT3 receptors in all the areas investigated. Ondansetron (4 mg/kg s. c) per se significantly increased the 5-HT3 receptor number in the areas used, the effect not being modified by co-administration with paracetamol. On the other hand, CP 93129 (2 mg/kg s. c.) significantly prevented the effect of paracetamol in both algesimetric tests used. Conclusions: Our data indicate that 5-HT1B but not 5-HT3 receptors are involved in the antinociceptive effect of paracetamol in our experimental conditions

Smooth cutoff formulation of hierarchical reference theory for a scalar phi4 field theory

The phi4 scalar field theory in three dimensions, prototype for the study of phase transitions, is investigated by means of the hierarchical reference theory (HRT) in its smooth cutoff formulation. The critical behavior is described by scaling laws and critical exponents which compare favorably with the known values of the Ising universality class. The inverse susceptibility vanishes identically inside the coexistence curve, providing a first principle implementation of the Maxwell construction, and shows the expected discontinuity across the phase boundary, at variance with the usual sharp cutoff implementation of HRT. The correct description of first and second order phase transitions within a microscopic, nonperturbative approach is thus achieved in the smooth cutoff HRT.Comment: 8 pages, 4 figure

The smooth cut-off Hierarchical Reference Theory of fluids

We provide a comprehensive presentation of the Hierarchical Reference Theory (HRT) in the smooth cut-off formulation. A simple and self-consistent derivation of the hierarchy of differential equations is supplemented by a comparison with the known sharp cut-off HRT. Then, the theory is applied to a hard core Yukawa fluid (HCYF): a closure, based on a mean spherical approximation ansatz, is studied in detail and its intriguing relationship to the self consistent Ornstein-Zernike approximation is discussed. The asymptotic properties, close to the critical point are investigated and compared to the renormalization group results both above and below the critical temperature. The HRT free energy is always a convex function of the density, leading to flat isotherms in the two-phase region with a finite compressibility at coexistence. This makes HRT the sole liquid-state theory able to obtain directly fluid-fluid phase equilibrium without resorting to the Maxwell construction. The way the mean field free energy is modified due to the inclusion of density fluctuations suggests how to identify the spinodal curve. Thermodynamic properties and correlation functions of the HCYF are investigated for three values of the inverse Yukawa range: z=1.8, z=4 and z=7 where Monte Carlo simulations are available. The stability of the liquid-vapor critical point with respect to freezing is also studied.Comment: 23 pages, 15 figures, 1 tabl