Is there a causal relation between mathematical creativity and mathematical problem-solving performance?

The relationship between mathematical creativity (MC) and mathematical problem-solving performance (MP) has often been studied but the causal relation between these two constructs has yet to be clearly reported. The main purpose of this study was to define the causal relationship between MC and MP. Data from a representative sample of 480 eighth-grade students were analysed using a cross-lagged panel correlation (CLPC) design. CLPC attempts to rule out plausible alternative explanation of a causal effect. The result suggests that significant predominant causal relationship was found between MC and MP. It indicates that MP was found to be a cause of MC than the converse.     

Synthesis and spectroscopic characterization of transition metal complexes of a 12-membered tetraaza [N<Subscript>4</Subscript>] macrocyclic ligand and their biological activity

Cobalt(II), nickel(II) and copper(II) complexes are synthesized with 1,3,7,9-tetraaza- 4,6,10,12-tetraphenyl-2,8-dithiacyclododecane, a tetradentate ligand (L) and characterized by elemental analysis, molar conductance measurements, magnetic susceptibitity measurements, mass, i.r., electronic and e.p.r. spectral studies. All the complexes are non-electrolytes so they may be formulated as [M(L)X₂] [where, M = Co(II), Ni(II) and Cu(II) and X = Cl⁻ and NO ₃ ⁻ ]. All the complexes are of high spin type. On the basis of i.r., electronic and e.p.r. spectral studies an octahedral geometry has been assigned for Co(II) and Ni(II) complexes and tetragonal geometry for Cu(II) complexes. The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been screened in vitro against two different species of bacteria and plant pathogenic fungi.     

The influence of an epitaxial CoSi2 layer on diffusion of B and Sb in underlying Si during oxidation

The effect of an epitaxial 20 nm thick CoSi₂ layer on the diffusion of B and Sb in Si is investigated during oxidation and is compared to thermal diffusion in Si. B and Sb doping superlattices (DSLs) were grown by molecular beam epitaxy (MBE). They consisted of six spikes with peak concentrations of about 10¹⁸ cm^–3 (B) and about 10¹⁹ cm^–3 (Sb) and peak centres spaced 100 nm apart. The shallowest spike was capped with 100 nm of Si followed by 20 nm of CoSi₂ grown by molecular beam allotaxy (MBA). Oxidation in dry O₂ and annealing in pure N₂ were performed at temperatures of 800?°C to 1200?°C. Concentration depth profiles were measured by secondary ion mass spectrometry (SIMS). The results showed that the diffusion of B and Sb in Si was markedly different for specimens with or without a CoSi₂ layer. Oxidation enhanced diffusion (OED) of B and oxidation retarded diffusion (ORD) of Sb was observed for specimens without a CoSi₂ layer. The effect of CoSi₂ layer was a strong retardation of B diffusion and an enhancement of Sb diffusion. The B diffusivity was retarded by a factor of 2–10 as compared to the thermal diffusivity and by a factor of 20–100 as compared to the corresponding diffusivity for oxidation of Si without a CoSi₂ layer. Sb diffusivity was enhanced by a factor of 2 with respect to thermal diffusivity and by about a factor of 5 as compared to the case without a CoSi₂ layer.     

Synthesis and characterization of stoichiometric NiCo nano particles dispersible in both aqueous and non aqueous media

Oleic acid (OA) coated stoichiometric NiCo (50:50) nanoparticles, with and without polyvinylpyrrolidone (PVP) coating, dispersible in aqueous and non aqueous media have been synthesized by a polyol process for the first time. Structural studies by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed the formation of an impurity free face centred cubic phase NiCo alloy. EDS analysis confirmed nearly 50:50 alloy composition. The magnetization, as a function of field and temperature, of these samples showed a soft ferromagnetic nature. The novelty of our method is that the particles are dispersible in non aqueous and aqueous media, which will facilitate preparation of films of these particles.     

Nano-graphitic clustering and break down of phonon selection rule in diamond-like carbon films

Diamond-like carbon films are deposited on silicon substrates at different substrate bias using ECR-CVD technique. Raman spectroscopic studies show the presence of broad G and D peaks. In contrast to the position of D peak, the G peak shows a systematic red-shift with increase in the bias voltage. From the analysis it is found that an increase in bias voltage decreases the sp² cluster diameter. Furthermore, two additional Raman peaks at around 690 and 880 cm^?1 are also observed. These peaks, forbidden in the first order Raman scattering, arise due to the breakdown of phonon selection rule in graphitic nanoclusters.     

Poly-β-hydroxybutyrate Production by Fast-Growing Rhizobia Cultivated in Sludge and in Industrial Wastewater

In our study, the potential of producing polyhydroxybutyrate (PHB) by cultivating fast-growing rhizobia (Sinorhizobium meliloti, Rhizobium leguminosarum bv. viciae, R. leguminosarum bv. phaseoli and R. leguminosarum bv. trifolii) in sludge and in industrial wastewater was evaluated. Results confirmed the possibility of using sludge as media for rhizobial growth. During growth, substantial quantity of PHB was accumulated and yields varied depending on the media and rhizobial species. Growing in sludge, PHB production did not exceed 3.7% w/w for all strains at the end of experiment (after 72 h). During the growth of S. meliloti, PHB yield varied and the maximum value reached 7.27% w/w after 60 h, with 1% Total Suspend Solid (TSS) sludge. Alkaline sludge pre-treatment affects rhizobial growth but did not improve the PHB accumulation. While growing S. meliloti in industrial wastewater, the PHB yields varied and the highest value was obtained with slaughterhouse wastewater (10.7% w/w) after 35 h of growth. Therefore, this work shows the potential of exploiting PHB production by rhizobia growing in wastewater or sludge which could be applied to bioplastic industry, and confirms the potential of these recyclable wastes for high production of rhizobial cells useable for legumes inoculants production. This study provides an environmentally sound way of sludge and wastewater management and use in diverse biotechnological applications.     

Absorption and emission spectroscopic characterisation of 8-amino-riboflavin

The flavin dye 8-amino-8-demethyl-d-riboflavin (AF) in the solvents water, DMSO, methanol, and chloroform/DMSO was studied by absorption and fluorescence spectroscopy. The first absorption band is red-shifted compared to riboflavin, and blue-shifted compared to roseoflavin (8-dimethylamino-8-demethyl-D-riboflavin). The fluorescence quantum yield of AF in the studied solvents varies between 20% and 50%. The fluorescence lifetimes were found to be in the 2–5 ns range. AF is well soluble in DMSO, weakly soluble in water and methanol, and practically insoluble in chloroform. The limited solubility causes AF aggregation, which was seen in differences between measured absorption spectra and fluorescence excitation spectra. Light scattering in the dye absorption region is discussed and approximate absorption cross-section spectra are determined from the combined measurement of transmission and fluorescence excitation spectra. The photo-stability of AF was studied by prolonged light exposure. The photo-degradation routes of AF are discussed.     

Structural phase transitions in Zn(CN)2 under high pressures

High pressure behavior of zinc cyanide (Zn(CN)₂) has been investigated with the help of synchrotron-based X-ray diffraction measurements. Our studies reveal that under pressure this compound undergoes phase transformations and the structures of the new phases depend on whether the pressure is hydrostatic or not. Under hydrostatic conditions, Zn(CN)₂ transforms from cubic to orthorhombic to cubic-II to amorphous phases. In contrast, the non-hydrostatic pressure conditions drive the ambient cubic phase to a partially disordered crystalline phase, which eventually evolves to a substantially disordered phase. The final disordered phase in the latter case is distinct from the amorphous phase observed under the hydrostatic pressures.