Natural convection in an inclined quadrantal cavity heated and cooled on adjacent walls

Natural convective flow and heat transfer in an inclined quadrantal cavity is studied experimentally and numerically. The particle tracing method is used to visualize the fluid motion in the enclosure. Numerical solutions are obtained via a commercial CFD package, Fluent. The working fluid is distilled water. The effects of the inclination angle, ? and the Rayleigh number, Ra on fluid flow and heat transfer are investigated for the range of angle of inclination between 0° ? ? ? 360°, and Ra from 10⁵ to 10⁷. It is disclosed that heat transfer changes dramatically according to the inclination angle which affects convection currents inside, i.e. flow physics inside. A fairly good agreement is observed between the experimental and numerical results.     

Determination of uric acid and creatinine in human urine using hydrophilic interaction chromatography

Uric acid is the end-product of purine metabolism and a major antioxidant in humans. The concentrations of uric acid in plasma and urine are associated with various diseases and routinely measured in clinical and biomedical laboratories using enzymatic conversion and colorimetric measurement. In this study a hydrophilic interaction chromatographic (HILIC) method was developed for simultaneous determination of uric acid and creatinine, a biomarker of urine dilution and renal function, in human urine. Urine samples were pretreated by dilution, protein precipitation, centrifugation and filtration. Uric acid and creatinine were separated from other components in urine samples and quantified using HILIC chromatography. A linear relationship between the ratio of the peak area of the standards to that of the internal standard and the concentration of the standards was obtained for both uric acid and creatinine with the square of correlation coefficients >0.999 for both analytes. The detection limits were 0.04 μg/mL for creatinine and 0.06 μg/mL for uric acid. The described HILIC method has proved to be simple, accurate, robust and reliable.     

On the Geometry of the （1, 1）-Tensor Bundle with Sasaki Type Metric

Curvature properties are studied for the Sasaki metric on the (1,1) tensor bundle of a Riemannian manifold. As an application, examples of almost para-Nordenian and para-K(a)hler-Nordenian B-metrics are constructed on the (1,1) tensor bundle by looking at the Sasaki metric. Also, with respect to the para-Nordenian B-structure, paraholomorphic conditions for the complete lifts of vector fields are analyzed.     

Size-Dependent HCl Generation of PVC/SiO2 Micro- and Nanocomposites

In this study HCl generation of polyvinyl (chloride) (PVC)/SiO₂ composites during its combustion was investigated. SiO₂ with different particle sizes were used as HCl absorbers and their HCl uptake ability results were compared to that of CaCO₃. It was found that the amount of released HCl gas during PVC combustion decreased in the presence of SiO₂. The HCl uptake ability of SiO₂ improved with decreasing of its particle size. Although thermogravimetric analysis (TGA) results showed that SiO₂ particles decreased the first thermal degradation temperature (T _onset) of PVC by initiating dehydrochlorination of PVC at lower temperatures, SiO₂ particles had more effective HCl uptaking ability than that of CaCO₃. Scanning electron microscopy (SEM) micrographs showed that some aggregates whose size was less than 100 nm were formed when Si-25 nm was used as filler. When SiO₂ with micron size was added to PVC as filler, more uniform and better distribution of the SiO₂ on the surface was observed.     

Quantum shape effects and novel thermodynamic behaviors at nanoscale

Thermodynamic properties of confined systems depend on sizes of the confinement domain due to quantum nature of particles. Here we show that shape also enters as a control parameter on thermodynamic state functions. By considering specially designed confinement domains, we demonstrate how shape effects alone modify Helmholtz free energy, entropy and internal energy of a confined system. We propose an overlapped quantum boundary layer method to analytically predict quantum shape effects without even solving Schrödinger equation or invoking any other mathematical tools. Thereby we reduce a thermodynamic problem into a simple geometric one and reveal the profound link between geometry and thermodynamics. We report also a torque due to quantum shape effects. Furthermore, we introduce isoformal, shape preserving, process which opens the possibility of a new generation of thermodynamic cycles operating at nanoscale with unique features.     

On infinitesimal conformal transformations of the tangent bundles with the synectic lift of a Riemannian metric

The purpose of the present article is to investigate some relations between the Lie algebra of the infinitesimal fibre-preserving conformal transformations of the tangent bundle of a Riemannian manifold with respect to the synectic lift of the metric tensor and the Lie algebra of infinitesimal projective transformations of the Riemannian manifold itself.     

The development of porcelain foams lighter than water for heat isolation application

In this study, technological and heat isolation properties of porous ultra-lightweight porcelain foams were investigated. Traditional construction materials such as brick show good durability against environmental conditions. Bricks are also a good alternative compared to pumice blocks and autoclaved aerated concrete which are largely used as construction materials. Bricks are also more economical than the other construction materials. But they also have poorer thermal insulation properties. Among the construction material, XPS shows the best heat isolation properties. XPS (extruded polystyrene foam) is a polymeric material. Although XPS shows best heat insulation property, it easily flames. The aim of this study is developing porous porcelain isolation materials lighter than water by using a replication method and relatively better thermal isolation properties than the other construction materials.

     

Quantum oscillations in confined and degenerate Fermi gases. I. Half-vicinity model

We propose an analytical model for the prediction and accurate calculation of size and density dependent quantum oscillations in thermodynamic and transport properties of confined and degenerate Fermi gases. Our model considers only half-vicinity states of Fermi level. We show that the half-vicinity model quite accurately estimates quantum oscillations depending on confinement and degeneracy. Periods of quantum oscillations are even analytically expressed for one-dimensional case. Furthermore, similarities between functional behaviors of total occupancy variance and conventional density of states functions at Fermi level are discussed.