Multivariate regression estimates for finite populations

The theory on regression estimate based on one auxiliary variable has been extended to that for more than one auxiliary variable. It has been found that the multivariate regression estimate (MRE) is not unbiased in general. The form of the approximate standard error of MRE is the same as that of simple regression estimate based on one auxiliary variable with the exception that the multiple correlation coefficient replaces the total correlation coefficient in the expression. It has also been found that the precision of MRE is non-decreasing, rather usually increasing as the number of auxiliary variables correlated with the dependent variable increases, assuming sample size to be large compared to the number of auxiliary variables.     

Non-Darcy free convective flow along a vertical cylinder embedded in a porous medium with surface mass flux

The nonsimilar non-Darcian free-convection flow about a vertical cylinder with impermeable surface embedded in a saturated porous medium, where surface temperature of the cylinder varies as x^m, a power function of distance from the leading edge, has been studied by employing the implicit finite-difference method together with the Newton's quasilinearization technique. In the present investigation, effects of the surface mass flux together with the inertial effects on the rate of heat transfer at the surface, on the velocity distribution, and on the temperature distribution are shown graphically.     

Optical implementation of an efficient modified signed-digit trinary addition

Efficient parallel schemes for carry-propagation-free addition of modified signed-digit trinary numbers are presented. The necessary minterms for implementation using an optical programmable logic array area are derived. The proposed schemes require only a truth table of 25 entries compared with an earlier scheme of 625 entries. The proposed schemes are amenable to optical implementation. Experimental results using an optical programmable logic array are demonstrated. The experiments show the problems of noise and crosstalk. This suggests some dc bias is necessary to increase the signal-to-noise ratio of the optical circuit.     

Synthesis and characterization of ruthenium(II) complexes of the NNS-donor Schiff-base derived from 2-methyl-2-(2-pyridyl)benzothiazoline

Transition Metal Chemistry -     

Preparation of a Novel Agarose-Salen Adsorbent,and its Use for Efficient Column Preconcentration and Flame AAS Determination of Lead in Water

A cross-linked agarose (Novarose) support was chemically modified with a novel salen-type Schiffs base; 2,2-[1,2-ethandiyl bis(nitrilimethylidyne)] bis(orthocresol) and was used to develop an efficient, simple and low-cost method for matrix separation and preconcentration of lead in water. The binding capacity of the adsorbent, packed in a 6.5mm i.d. glass column, was tested for different metal ions, and a capacity of 4973 (±95) µg per mL of packed adsorbent for triplicate measurements was obtained for lead at pH 6.0.The effects of pH, ionic strength, buffer concentration, sample volume, eluent concentration and volume, and matrix ions on the column recovery of Pb²⁺ were carefully studied. Quantitative recoveries were obtained for the analyte in a pH range of 5.5 to 7.0. Enrichment volumes up to 300mL and ionic strengths up to 0.5molL^–1 had no significant effect on the recovery of Pb²⁺. The method also tolerated relatively high concentrations of matrix ions such as Ca²⁺, Mg²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Mg²⁺ and Cd²⁺ with no considerable effect on the analytes signal. A few mL of 0.4molL^–1 hydrochloric acid was sufficient for quantitative elution of the analyte from a 0.5mL column before its flame AAS determination. Preconcentration factors up to 60 and a detection limit of 2.5µgL^–1 were obtained for the method. The precision, expressed as relative standard deviation, was 2.9% (at 100µgL^–1) calculated from six replicate measurements. The method was successfully applied to the determination of Pb²⁺ in some river and spiked river water samples with good precision.     

Tritopic (cascade) and ditopic complexes of halides with an azacryptand

Structural aspects of the binding of halides in the octaaza cryptand (1,4,11,14,17,24,29,36-octa-azapentacyclo[12.12.12.2(6,9).2(19,22).2(31,34)]-tetratetraconta-6(43),7,9(44),19(41),20,22(42),31(39),32,34(40)-nonaene, N(CH2CH2NHCH2-p-xylyl-CH2NHCH2CH2)3N), L1, were examined for fluoride, chloride, and bromide. Crystallographic results for two different fluoride complexes indicated cascade-like coordination, with two fluoride ions inside the tren-based cavity, bridged by a water molecule. In the two different chloride structures, a single chloride and a water molecule occupied the cavity. The bromide structure contained two crystallographically independent cationic cryptands. Unit A consisted of a bromide on one side of the cavity and three disordered water molecules situated between the cryptand arms on the other side. Unit B also had a bromide inside the cavity at one side, but a single molecule of water was centered at the other side of the cavity. Association constants for the three ions, determined by NMR titrations in aqueous solution at pH 5, revealed log Ka=3.15(5), 3.37(3), and 3.34(4) for fluoride, chloride, and bromide, respectively.