Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Synthesis and crystal structure of the high-pressure iron borate α-FeB2O4

The high-pressure iron borate α-FeB₂O₄ was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. The monoclinic iron borate crystallizes with eight formula units in the space group P2₁/c with the lattice parameters a=715.2(2), b=744.5(2), c=862.3(2) pm, and β=94.71(3)°. The compound is built up exclusively from corner-sharing BO₄-tetrahedra, isotypic to the monoclinic phases β-SrGa₂O₄, CaAl₂O₄-II, and CaGa₂O₄. Additionally, the structure is closely related to the orthorhombic compound BaFe₂O₄. The structure consists of layers of six-membered rings, which are interconnected to a three-dimensional network. The iron cations are coordinated by six and seven oxygen atoms. Next to synthesis and crystal structure of the new high-pressure borate, structural coherences to other structure types are discussed.     

Permanently oriented antibody immobilization for digoxin determination with a flow-through fluoroimmunosensor

This paper reports a new flow-through fluoroimmunosensor, the function of which is based on antibodies immobilized on an inmunoreactor of controlled-pore glass (CPG), for determination of digoxin, used in the treatment of congestive heart failure and artery disease. The immunosensor has a detection limit of 1.20 microg L(-1) and provides high reproducibility (RSD=4.5% for a concentration of 0.0025 mg L(-1), and RSD=6.7% for 0.01 mg L(-1)). The optimum working concentration range was found to be 1.2 x 10(-3)-4.0 x 10(-2) mg L(-1). The lifetime of the immunosensor was about 50 immunoassays; if stored unused its lifetime can be extended to three months. A sample speed of about 10-12 samples per hour can be attained. Possible interference from substances with structures similar to digoxin (morphine, heroin, tebaine, codeine, pentazocine and narcotine) was investigated. No cross-reactivity was seen at the highest digoxin: interferent ratio studied (1:100). The proposed fluoroimmunosensor was successfully used to determine digoxin concentrations in human serum samples.     

High-pressure synthesis and characterization of the alkaline earth borate β-BaB4O7

The new orthorhombic barium borate β-BaB₄O₇ was synthesized under high-pressure/high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C, starting from stoichiometric mixtures of the binary oxides. β-BaB₄O₇ crystallizes in space group Pmnb with Z = 2 and lattice parameters a = 1099.4(2), b = 901.7(2), c = 430.73(9) pm, R1 = 0.0199, and wR2 = 0.0406 (all data). The network-structure is built up exclusively from BO₄-tetrahedra, linked via common corners. Its structural differences to the ambient-pressure phase α-BaB₄O₇ and structural agreements with the isotypic high-pressure phases β-MB₄O₇ (M = Ca, Hg, Sn) and the ambient-pressure phases MB₄O₇ (M = Sr, Pb, Eu) are discussed. β-BaB₄O₇ and a hypothetical BaB₄O₇ in the β-MB₄O₇ (M = Ca, Hg, Sn) structure were studied as high-pressure phases of α-BaB₄O₇, using density functional calculations. The transition pressure of α-BaB₄O₇ into the structure of β-BaB₄O₇ was calculated to 1.5 GPa; the transition pressure of β-BaB₄O₇ into BaB₄O₇ in the β-MB₄O₇ (M = Ca, Hg, Sn) structure to 7.5 GPa.