Etude de niobates de structure GTB par absorption infra-rouge et diffusion raman

Infrared and Raman spectra of GTB niobates MNb₇O₁₈(M = Tl, K, Cs, Rb) were recorded in the region 1100-100 cm^?1. All of them are similar and an assignment of the observed frequencies is proposed. Raman lines at about 1000 cm^?1 seem to confirm the existence of shear planes.     

Luminescence of Cu<Superscript>+ </Superscript>in halosulphate phosphor

Ultraviolet photo-excited luminescence from Cu-doped halosulphate phosphors has been investigated. The intense emission of the spectrum is assigned to electronic transitions 3d⁹4s¹ → 3d¹⁰ in Cu⁺ ions. Increase in photoluminescence (PL) peak intensity suggesting that Cu plays an important role in PL emission in the present matrix. However, limited hosts with Cu⁺ as luminescence center were studied due to difficulties in incorporating it in a luminescence form. Cu-doped halosulphate phosphors were synthesized by wet chemical method. X-ray diffraction and PL characterization of phosphors has been reported in this article. The article discusses the luminescence of Cu⁺ and the simple method of incorporation in various new hosts.     

Evaluation of Generating System Reliability Indices Under Limited Repair Facility

A generating system having n units, where each unit is represented by a 2-state device, will have more than 2n possible states when repair facility of the system is limited, i.e. number of repair crews is less than the number of units. When the number of units failed is more than the number of repair crews available, the most recent failures queue for repairs. This paper gives a general equation to determine the number of system states under limited repair facility and an approximate technique to determine the probabilities of system states and reliability indices of the system.     

Lung tumour incidence in mice treated with hydrazine sulphate

Lung tumour incidence in mice fed with hydrazine sulphate (1.1 mg/day/mouse) was studied in male and female mice of Swiss, Strong "A" and F1 cross of ICRC (female) X C3H (Jax) (male), as well as in C17 males. Swiss strain mice showed 100% lung adenocarcinomas. None of the treated mice of different strains had liver tumours. Hydrazine sulphate also induced adenocarcinomas of lung in Strong "A" and F1 cross of ICRC females X C3H (Jax) males but it produced lymphomas of lung in C17 strain. Female mice of Swiss strain and F1 hybrids showed greater susceptibility to hydrazine sulphate than the males. It was interesting to observe that protein and vitamin B deficiency in the diet shortened the tumour induction period in Swiss strain mice.     

Transient axonal branching in the developing corpus callosum

During development, there is a transient overproduction of axons in the corpus callosum; this overproduction of axons is due, in part, to a transient excess of neurons that send an axon through the corpus callosum. However, transient axonal branching could also contribute to the developmental overproduction of callosal axons. To investigate this possibility, we filled developing callosal axons in the Syrian hamster with the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). Light microscopic analysis showed that, indeed, developing callosal axons branch transiently in the hamster: branching was robust on postnatal day 0 (P0) and P3 (P0 = the first 24 hr after birth), less prominent on P6 and P8, and absent by P11. Immature callosal axons branched before or after crossing the midline and at all rostral-caudal and medial-lateral levels within the corpus callosum. The majority of callosal axon collaterals that were contained within individual 100-micron-thick sections were relatively short (mean = 15.1 microns) but some collaterals extended up to approximately 135 microns from the main axon trunk before passing out of the section in which they were observed. Nearly all of the collaterals emanated from the main axon trunk; higher-order collaterals were rare. Some callosal axon trunks had multiple collaterals. Branching callosal axons originated from multiple cortical areas, including area 17. Electron microscopic observations indicated that the processes designated as axon collaterals by light microscopic criteria would have been included in electron microscopic counts of developing callosal axons. Some callosal axon trunks and branches had ultrastructural features that suggested they were degenerating. In cats, developing callosal axons branch on embryonic day 57 (E57; the first 24 hr after conception = E0) and P0. Thus, it is likely that transient branching of immature callosal axons is a generalized feature of mammalian cortical development and that it contributes to the overproduction of callosal axons, albeit perhaps to varying degrees, in multiple species.     

Probing Site Symmetry Around Eu3+ in Nanocrystalline ThO2 Using Time Resolved Emission Spectroscopy

ThO₂:Eu³⁺ nanoparticles were synthesized at 300°C by combustion route using urea as a fuel and characterized by thermogravimetric/differential thermal analysis, X‐ray diffraction, transmission electron microscopy, and photoluminescence techniques. To investigate the effect of annealing temperature, as synthesized powder were heated further at 500°C, 700°C, and 900°C. It was observed that extent of asymmetry around Eu³⁺ at 700°C/900°C is very high as compared to as‐prepared or 500°C annealed sample. Based on the time resolved emission spectroscopic investigations, it was inferred that two different types of Eu³⁺ ions were present in the ThO₂ nanoparticles. In ThO₂ structure, Eu³⁺ ions occupy two sites; cubic (O_h) and noncubic (<C_2v) as can be confirmed from our emission studies. Short‐lived species T₁ (~1.3–3.4 ms) predominates at higher annealing temperature arises because of Eu³⁺ ions occupying noncubic (<C_2v) sites without inversion symmetry, whereas long‐lived species T₂ (~4.6–6.6 ms) can be ascribed to Eu³⁺ ions occupying cubic sites (O_h) with inversion symmetry.