Rapidity dependence of global polarization in heavy ion collisions

We use a geometric model for hadron polarization in heavy ion collisions with an emphasis on the rapidity dependence.The model is based on the model of Brodsky,Gunion,and Kuhn,as well as the Bjorken scaling model.We make predictions regarding the rapidity dependence of global Λ polarization in the collision energy range of 7.7-200 GeV by assuming the rapidity dependence of two parameters,κ and <ρτ>. The predictions can be tested by future beam-energy-scan experiments at the Relativistic Heavy Ion Collider of Brookhaven National Lab.     

75th anniversary of Vladimir K. Baev

Anniversary Dates

75th anniversary of Vladimir K. Baev     

Tailoring mixed proton-electronic conductivity of BaZrO3 by Y and Pr co-doping for cathode application in protonic SOFCs

BaZr_0.8 − xPr_xY_0.2O_3 − δ (BZPYx, 0.1 ≤ x ≤ 0.4) perovskite oxides were investigated for application as cathode materials for intermediate temperature solid oxide fuel cells based on proton conducting electrolytes (protonic-SOFCs). The BZPYx reactivity with CO₂ and water vapor was evaluated by thermogravimetric and X-ray diffraction analyses, and good chemical stability was observed for each BZPYx composition. Conductivity measurements of BZPYx sintered pellets were performed as a function of temperature and p_O2 in humidified atmospheres, corresponding to cathode operating condition in protonic-SOFCs. Different conductivity values and activation energies were measured depending on the Pr content, suggesting the presence of different charge carriers. For all the compositions, the partial electronic conductivity, calculated from conductivity measurements at different p_O2, increased with increasing the temperature from 500 to 700 °C. Furthermore, the larger the Pr content, the larger the electronic conductivity. BaZr_0.7Pr_0.1Y_0.2O_3 − δ and BaZr_0.4Pr_0.4Y_0.2O_3 − δ showed mostly pure proton and electron conductivity, respectively, whereas the intermediate compositions showed mixed proton/electronic conductivity. Among the two mixed proton/electronic conductors, BaZr_0.6Pr_0.3Y_0.2O_3 − δ presented the larger conductivity, which coupled with its good chemical stability, makes this perovskite oxide a candidate cathode materials for protonic-SOFCs.     

Generalized Hopf Bifurcation for Planar Vector Fields via the Inverse Integrating Factor

In this paper we study the maximum number of limit cycles that can bifurcate from a focus singular point p ₀ of an analytic, autonomous differential system in the real plane under an analytic perturbation. We consider p ₀ being a focus singular point of the following three types: non-degenerate, degenerate without characteristic directions and nilpotent. In a neighborhood of p ₀ the differential system can always be brought, by means of a change to (generalized) polar coordinates (r, θ), to an equation over a cylinder in which the singular point p ₀ corresponds to a limit cycle γ ₀. This equation over the cylinder always has an inverse integrating factor which is smooth and non-flat in r in a neighborhood of γ ₀. We define the notion of vanishing multiplicity of the inverse integrating factor over γ ₀. This vanishing multiplicity determines the maximum number of limit cycles that bifurcate from the singular point p ₀ in the non-degenerate case and a lower bound for the cyclicity otherwise. Moreover, we prove the existence of an inverse integrating factor in a neighborhood of many types of singular points, namely for the three types of focus considered in the previous paragraph and for any isolated singular point with at least one non-zero eigenvalue.     

System Dynamics Modelling for Residential Energy Efficiency Analysis and Management

A System Dynamics model to simulate the substitution of installed household appliances by more efficient ones is presented. The model allows the construction of scenarios and also the analyses of several other issues such as: alternatives for technology penetration, electricity consumption growth, gas consumption growth and effects of pricing policies on various energy demands. The proposed methodology has been applied to assist the decision process in relation to gas penetration policies. The model also supports policy making on energy efficiency and it allows the calculation of total energy savings under different scenarios. Furthermore, government underpricing policies on tariffs and appliance acquisition (longer loan terms, lower interest rates and grace periods) may also be analysed.     

Photoelastic analysis of stresses around oblique holes

A three-dimensional photoelastic analysis was conducted to determine the magnitude and distribution of stresses around oblique holes in a uniaxially loaded plate. The holes were circular and inclined at angles of 45 deg and 60 deg with the faces of the plate. The plate-thickness-to-hole-diameter ratiot/D was 2.40. One end of each hole was blended to the face of the plate through a break radius equal to the radius of the hole. The plate dimensions were sufficiently large to simulate conditions of an infinite plate. The plates were loaded perpendicular to the plane of skewness. Stress distributions were obtained on sections perpendicular to the direction of loading. Results point to two critical areas of stress concentration: one at the acute-angle intersection of the hole and the surface of the plate and the other in the break-radius area. The stress concentrations in the latter area reach values of 4.6 and 6.7 compared to 3.6 and 4.5 at the acute-angle intersection, for the inclination angles of 45 deg and 60 deg, respectively. A simplified analysis used for the break-radius area gave results in agreement with the experiment. Thus, it was shown that break radii in oblique penetrations may have deleterious rather than beneficial effects. Comparison of results for the acute-angle intersection with existing theoretical and experimental values shows a definite and pronounced dependence of the stress-concentration factor on thickness-to-diameter ratio.     

Quasi-static properties of a photoviscoelastic material

This paper describes the results of mechanical and optical measurements in plasticized polyvinyl chloride under conditions of creep and relaxation at room temperature. It covers one task of a broader investigation aimed at developing experimental methods for viscoelastic stress analysis. The moiré method of strain analysis was found well suited for continuous recording of axial and transversal deformation in creep tests. The material exhibits linear viscoelastic behavior, both mechanical and optical. Strain, stress and birefringence measured from creep and relaxation tests gave straightline plots on log-log scale and, thus simple empirical formulas were possible to derive. The theoretical prediction that birefringence in a linear viscoelastic material not exhibiting flow can be expressed as a linear relationship of stress and strain was satisfactorily substantiated.     

Synthesis and pH‐Dependent Spectroscopic Behavior of 2,4,6‐Trisubstituted Pyridine Derivatives

Seven 2,4,6‐trisubstituted pyridine derivatives with N,N‐diethylaniline substituents at the 4‐position were synthesized, and their spectroscopic properties in the absence and presence of acid were studied. The spectral effects of protonation, molar absorptivities, pK_a values, and the structural origins of the observed spectral behavior were ascertained. The pyridine nitrogen was found to be more basic than the diethylamino nitrogen atom. Protonation of the pyridine ring nitrogen is associated with the appearance of a red‐shifted intramolecular charge transfer peak in the UV‐visible spectra. Favorable color indicating properties result from electron‐donating substitution at the 2 and 6 positions of pyridine, which provide a greater absorptivity of the red‐shifted peak associated with protonation of the pyridine nitrogen. These findings will assist in the design and optimization of these compounds for ion‐indicating and pH‐sensing applications.