[en] Pure and rare earth ions doped yttrium oxide (Y₂O₃) waveguide films were prepared by a simple sol-gel process and dip-coating technique. Y₂O₃ were successfully synthesized by hydrolysis of yttrium acetate. The structural evolution of Y₂O₃ films with annealing temperature was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, waveguide Raman spectroscopy and High-resolution transmission electron microscopy. The propagation loss of Y₂O₃ thin films at 632.8 nm measured by scattering-detection method is approximately 1.5 dB/cm. The fluorescence of Er³⁺ and Eu³⁺ doped Y₂O₃ waveguide thin films were studied under the waveguide configuration. The fluorescence intensities evolution with annealing temperature of Y₂O₃:Er³⁺ films has been studied and was explained by the multi-phonon non-radiative processes. Our results show that Y₂O₃ is a good host material for optically active waveguide thin films and sol-gel process is a useful method to derive pure and doped Y₂O₃ waveguide films

[en] The process of quenching of fluorescence from the ³P₀ state of Pr³⁺ in La/sub 0.72/Pr/sub 0.25/Nd/sub 0.03/F₃ due to cross relaxation to Pr and Nd ions has been investigated. The fluorescence decay of the ensemble of Pr ions after pulsed excitation is measured as a function of temperature in the (2-70)-K region. Cross relaxation occurs either directly or through a donor-donor transfer within the inhomogeneous line. Knowledge of the dynamics occurring within the inhomogeneous line derived from previous fluorescence line-narrowing experiments is used to analyze the cross-relaxation process from a microscopic viewpoint according to models for fluorescence decay in the presence of traps. In general the decay is consistent with an electric dipole-dipole transfer mechanism. At 2 K the decay can be well described by a direct transfer to Pr and Nd traps without donor-donor transfer. The temperature dependence of the decay at long times can be described for 35 < T < 70 K by the hopping model. The agreement with theory is much better if the cross relaxation to Nd ions is assumed to occur mainly via the lowest Stark level of the ⁴I/sub 9/2/ manifold

[en] Using a pseudopotential, weak-scattering formalism we calculate the driving force for electromigration by the vacancy mechanism in the hcp metals Zn, Cd, and Mg. The general formula is evaluated in a succession of approximate models to illustrate the influence of different physical effects. The final results are compared both with the experimental data and with a previous evaluation for Zn. Our form factors, which have been fit to low-temperature data and then scaled to account for volume changes near the melting point, yield an effective valence for the wind force of about twice the experimental value and only in qualitative agreement with the observed anisotropy. Possible resolutions are discussed

[en] In the present study, the texturing of bulk α-Fe/Nd₂Fe₁₄B nanocomposites produced from Nd-lean amorphous Nd_xFe_92.5−xCu_1.5B₆ (x=9 to 11.5 at%) via a hot deformation under a uniaxial stress of ∼350 MPa at 973 K has been studied. An enhanced (00l) texture of the hard phase is observed with increasing Nd content, which results in an increase in the magnetic anisotropy of the nanocomposite magnets. As a result, both the coercivity and the remanence of the magnets increase simultaneously with increasing Nd content from x=9–11.5 at%, yielding a significant enhancement of the maximum energy product from (BH)_max=13.2 to 17.5 MGOe in the direction parallel to stress axis. - Highlights: • Textured bulk α-Fe/Nd₂Fe₁₄B nanocomposites have been produced from Nd-lean alloys. • Nd content has an effect on the texturing of α-Fe/Nd₂Fe₁₄B nanocomposite magnets. • An enhanced (00l) texture of hard phase is observed with increasing Nd content. • Both the coercivity and remanence increase simultaneously with Nd content

[en] The electronic structure of recently discovered hollow-cage molecule Ti₈C₁₂ has been calculated and compared to similarly shaped hypothetical molecules M₈X₁₂ (M=metal and X=B, C, or N). The cohesion of the cage is related to the σ-bonding between M--X arising from d--sp hybridization. It is also shown that the cage can become electronically closed shell with all the valence electrons paired when the carbon is replaced by boron or nitrogen, e.g., in the formula of Sc₈B₁₂

[en] Linear chains of C_n (n=4 endash 21) in the presence of an external, static electric field are studied using ab initio methods. The results show that the polarization energy per atom increases with the number of atoms that are already incorporated in the chain. This size dependence will lead to a field-assisted growth of carbon atomic chains unraveled from the open tip of a carbon nanotube under a bias voltage. copyright 1996 The American Physical Society

[en] A study of the decay of hot and heavy composite nuclei produced in the violent collisions between ⁶³Cu and ²³²Th at 35A MeV is presented. The measurement of fission fragment correlations indicates that ∼ 70% of the projectile linear momentum can be transferred to the fissioning system. Heavy reaction products were observed at a laboratory angle of θ=6 degree in coincidence with neutrons, light charged particles, and intermediate mass fragments. The dynamical aspects of the collisions between the projectile and target nuclei were investigated using the computer code CHIMERA which is based upon the molecular dynamics concept. Asymptotic characteristics of the reaction products were confronted with results of calculations of the tandem CHIMERA plus GEMINI codes. The data and model comparisons show that a composite system of mass as high as 275 amu and with an excitation energy ∼ 1 GeV is formed in the most violent collisions. Some of the heavy reaction remnants are located on the fragment mass versus velocity plane inside the area where the evaporation residues resulting from the decay of the hot composite system are expected. A high neutron multiplicity associated with these events indicates their origin in the most dissipative events. However, a low cross section for the production of these remnants and the close similarity of their characteristics to the fission fragments do not allow more conclusive statements. copyright 1997 The American Physical Society

[en] The preparation of standards is possibly the single most important step in ensuring the clinical efficiency of an immunoassay. Therefore, there is a need for development of simple and efficient analytical methods to obtain analyte-free standards that resemble the original matrix. In particular, the determination of progesterone in milk and serum requires a standard completely free of the steroid, which becomes a very difficult task using conventional methods such as addition of charcoal or the use of special bovine milk. In this work, we report a procedure for the preparation of a progesterone- free standard using cloud point extraction and skim milk. The method involves the use of non-ionic surfactant (Triton X-114) as the extracting phase, and short centrifugation times. Different factors that can influence the extraction efficiency were evaluated using a radioimmunoassay (RIA) of progesterone in bovine milk. The RIA kit includes the use of a ¹²⁵I-labelled tracer purified by HPLC, a standard prepared with skim milk, and an anti-progesterone antiserum in solid phase. The method presented here can be used as a simple and low-cost alternative to obtain a standard containing progesterone at concentration levels below the detection limits of the immunoassay used.(Author)

[en] The influence of concentration and temperature on the luminescence properties of the Eu³⁺ activated X₁-Y₂SiO₅ are investigated for the first time. For high Eu³⁺ concentration, a cross relaxation process between Eu³⁺ ions results in the quenching of ⁵D₁ emission. At low temperature and high concentration, the excitation transfer between Eu³⁺ ions in the two sites enables the fluorescence of site 2 disappears entirely. In addition, the samples showed some interesting phenomenon related to size effect. (orig.)

[en] A study of the decay of heavy and hot composite system produced in the violent collision between the ⁶³Cu + ²³²Th at 35 MeV/u is presented. The measurement of fission fragment correlations indicates that above 70% of the projectile linear momentum can be transferred to the fissioning system. This suggests that the composite system of mass as high as 280 amu and with an excitation energy above 1 GeV is formed in the most violent collisions. Heavy reaction products are observed at a laboratory angle of θ=6 deg in the coincidence with the highest multiplicity of neutrons, light charged particles and intermediate mass fragments. None of these heavy reaction remnants can be unambiguously identified as an evaporation residue resulting from the decay of hot composite system. The dynamical aspects of collision between projectile and target nuclei are followed in terms of a computer code which is based upon the molecular dynamics concept. (authors). 13 refs., 3 figs