Experimental and theoretical investigation of the room-temperature photoluminescence of amorphized Pb(Zr,Ti)O3.

Ultrafine PbZr0.20Ti0.80O3 was amorphized through high-energy mechanical milling. The structural evolution through the amorphization process was accompanied by various characterization techniques, such as X-ray diffraction, Fourier-transformed IR spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. A strong photoluminescence was measured at room temperature for amorphized PbZr0.20Ti0.80O3, and interpreted by means of high-level quantum mechanical calculations in the density functional theory framework. Three periodic models were used to represent the crystalline and amorphized PbZr0.20Ti0.80O3, and they allowed the calculation of electronic properties that are consistent with the experimental data and that explain the appearance of photoluminescence.     

Analysis of Longitudinal Mode Suppression in a Fiber Ring Laser Containing Two Optical Filters

We report the results from the characterization and optimization of a stable erbium-doped fiber ring laser that uses two optical filters. The observed laser performance and the measured longitudinal mode patterns are presented. The influence of the combination of the two optical filters on the mode suppression is evaluated. We obtained the matched condition for operation of the optical filters that most improved the laser performance. An estimate of the relative intensity noise due to the introduction of the laser in a communication system is also presented. As a consequence of the mode suppression, a sharp laser linewidth narrowing is con firmed.     

Influence of a co-substituted A-site on structural characteristics and ferroelectricity of (Pb,Ba, Ca)TiO3 complex perovskites: analysis of local-, medium- and long-range order

Thin films of A-site co-substituted, PbTiO₃ (PTO) by Ba²⁺ and Ca²⁺, i.e., PBCT70, PBCT60, PBCT50 and PBCT40 were fabricated on Pt/Ti/SiO₂/Si substrates by chemical solution deposition. Structures of the samples were investigated from the viewpoint of local-, medium- and long-range order by X-ray absorption near structure (XANES), micro-Raman and infrared spectroscopies and by X-ray diffraction (XRD). The films thickness were determined by using field-emission scanning electron microscope. The experimental results demonstrate that BaO₁₂ clusters are the critical dominant ferroelectricity cause in PBCT thin films rather than CaO₁₂ clusters. XRD analysis which was applied to investigate the crystal symmetry indicates the absence of long-range structural distortion for samples at higher concentrations of Ba²⁺ and Ca²⁺. However, an analysis of structural medium- and local-range order such as infrared, micro-Raman and XANES spectroscopies revealed that symmetry changes are much more prominent; i.e., local structural distortions remain. Temperature-dependent dielectric permittivity measurements confirmed a decreasing ferroelectric-to-paraelectric phase transition temperature and showed a broad phase transition with an increase in BaO₁₂ and CaO₁₂ clusters. In addition, the lack of long-range polar ordering for the ferroelectric dipole caused by symmetry changes decreases the remanent polarization.     

A novel approach for the development of photoluminescent material

We report on several amorphous compounds based on different metal oxianions with intense photoluminescence at room temperature. These compounds were synthesised by a soft chemical process and deposited on Si (100) by a spin-coating technique. To select these different metal oxianions, a classic concept based on a metal oxide network former is used. We describe a minimum set of requirements to obtain an amorphous metal oxide with photoluminescence emission at room temperature. Received: 27 August 2001 / Accepted: 29 August 2001 / Published online: 20 December 2001     

Glottic Characteristics and Voice Complaint in the Elderly

This study evaluated the relationship between voice complaint and deviant vocal fold status with special regard to presbylarynx, in patients aged more than 60 years, with pharyngeal-laryngeal complaint. The material consisted of clinical histories and images obtained by laryngoscopies from protocols from the Larynx Institute-INLAR, Sao Paulo, Brazil, of 210 patients, 88 men and 122 women, aged more than 60 years, who had sought otorhinolaryngologic treatment. Indicative glottic characteristics of the presbylarynx, such as vocal fold bowing, prominence of vocal processes, and spindle-shaped glottic chink, were analyzed. The increase in mass, leukoplakia, and other vocal fold alterations, distinct from these two, grouped as miscellaneous, as well as the presence or absence of voice complaint were also analyzed. Vocal fold bowing, prominence of vocal processes, and spindle-shaped glottic chink showed a strong correlation among each other. The presence of presbylarynx was accompanied by less voice complaint than the presence of vocal fold mucosa alterations, which in turn are more common where an absence of presbylarynx exists.     

Symmetry controlled spin polarized conductance in au nanowires

The fact that the resistance of propagating electrons in solids depends on their spin orientation has led to a new field called spintronics. With the parallel advances in nanoscience, it is now possible to talk about nanospintronics. Many works have focused on the study of charge transport along nanosystems, such as carbon nanotubes, graphene nanoribbons, or metallic nanowires, and spin dependent transport properties at this scale may lead to new behaviors due to the manipulation of a small number of spins. Metal nanowires have been studied as electric contacts where atomic and molecular insertions can be constructed. Here we describe what might be considered the ultimate spin device, namely, a Au thin nanowire with one Co atom bridging its two sides. We show that this system has strong spin dependent transport properties and that its local symmetry can dramatically change them, leading to a significant spin polarized conductance.     

Continuous Soluble Ziegler‐Natta Ethylene Polymerizations in Reactor Trains, 3 – Influence of Operating Conditions upon Process Performance

The behavior of continuous solution ethylene/but‐1‐ene polymerizations through Ziegler‐Natta catalysts is analyzed, based on a previously developed mathematical model. In order to do that, dynamic simulations are carried out and process responses are analyzed as functions of process operating policies and flowsheet configuration, at conditions that resemble the actual operation of industrial sites. It is shown that system responses are highly nonlinear and very sensitive to disturbances of the operating conditions and that catalyst decay is of fundamental importance for proper understanding of process behavior. Results indicate that mixing conditions inside the reactor vessels exert a significant impact upon the final polymer quality and can be manipulated for in‐line control of final resin properties. Finally, it is shown that the development of feed policies, based on the use of lateral feed streams, allows the simultaneous control of melt flow index, stress exponent and polymer density of the final polymer resin.

     

Determination of low‐molecular‐weight amines and ammonium in saline waters by ion chromatography after their extraction by steam distillation

A new method was developed for the determination of ammonium ion, monomethylamine and monoethylamine in saline waters by ion chromatography. Steam distillation was used to eliminate matrix interferences. Variables such as distillation time, concentration of sodium hydroxide solution and analyte mass were optimized by using a full two‐level factorial (2³) design. The influence of steam distillation on the analytical curves prepared in different matrices was also investigated. Limits of detection of 0.03, 0.05 and 0.05 mg/L were obtained for ammoniumion, monomethylamine and monoethylamine, respectively. Saline water samples from the Brazilian oil industry, containing sodium and potassium concentrations between 2.0–5.2% w/v and 96–928 mg/L, respectively, were analyzed. Satisfactory recoveries (90–105%) of the analytes were obtained for all spiked samples, and the precision was ≤ 7% (n = 3). The proposed method is adequate for analyzing saline waters containing sodium to ammoniumion, monomethylamine and monoethylamine concentration ratios up to 28 000:1 and potassium to ammonium, monomethylamine and monoethylamine concentration ratios up to 12 000:1.     

Vocal Nodules and Laryngeal Morphology

Our purpose was to study the occurrence of vocal fold nodules under conditions of habitual vocal abuse associated with increased laryngeal muscle tension, to identify the existence of a relationship between vocal nodules and laryngeal morphology. We studied one group of 30 subjects with vocal nodules, 18 to 50 years old, who were compared with two control groups, one of females and one of males, consisting of 30 subjects each. The parameters evaluated were: type of vocal folds coaptation, glottic proportion (GP) and abduction angle (AA), obtained by videotelelaryngoscopy. In the nodules group, the larynges presented a mean value of GP similar to that of the female group, both of which were lower than the mean GP value of the male group. On the other hand, the mean AA was lower than the one in the female group, and closer to the one in the male group. We concluded that vocal nodules were present only in larynges with a predominantly young female morphology, with functional limitations of abduction.