DC-Amplifier-Input-Offset-Voltage Control in a Constant-Temperature Thermoresistive-Sensor-Measurement Instrument

In this paper, the effect of dc amplifier input offset voltage on the static and dynamic performances of a generic constant-temperature thermoresistive-sensor-feedback circuit (CTC) is reviewed. A negative-feedback automatic control circuit for the input offset voltage is proposed in order to assure a stable operation of the CTC and to obtain optimal response time. Experimental evaluation results of the proposed circuit performance are presented     

Thermal and Optical Properties of Yb3+- and Nd3+-Doped Phosphate Glasses Determined by Thermal Lens Technique

In this work, we study the thermal and optical properties of ion-doped phosphates glasses using the thermal lens (TL) technique. Three samples were characterized: Nd³⁺-doped Q-98; Nd³⁺-doped Q-100; and Yb³⁺-doped QX. We report multiwavelength TL measurements for a more accuracy determination of the fluorescence quantum efficiency and temperature coefficient of the optical path length change (ds/dT). In Nd-doped glasses, it was carried out using four discrete excitation wavelengths (between 514 and 872 nm) chosen to match with the ion absorption lines. In Yb-doped glass, the spectrum of heat generated along the Yb³⁺ transition (² F _5/2rarr² F _7/2) was obtained. In addition, parameters as thermal diffusivity and conductivity, thermal loading, etc were achieved. The advantages to obtain fluorescence quantum efficiency using the TL technique, mainly in Yb³⁺ doped materials, which are normally overestimated due to radiation trapping effect, are presented. The accuracy knowledge of these parameters is very important for design of high-power solid-state lasers, since these properties are directly related to the heat generation.     

Antibiofilm activity of the essential oil of citronella (Cymbopogon nardus) and its major component,geraniol, on the bacterial biofilms of Staphylococcus aureus

Food Science and Biotechnology - Medicinal plants with antimicrobial action have been investigated for uses against biofilms, among which, Cymbopogon nardus, citronella, stands out as a promising...     

Feedback control method for estimating the oxygen uptake rate inactivated sludge systems

The measurement and utilization of the respiration rate or oxygen uptake rate (OUR) is very important in activated sludge system control. It provides information about the quality of the influent, activated sludge quality and can indicate the presence of toxic elements that can poison the system. The existing methods for continuously measuring and estimating the OUR have, generally, a long sampling interval of a few minutes. An alternative respiration rate meter with much shorter response time is proposed. The results of simulation studies, as well as experimental results of a microcontroller based data acquisition system connected to a PC, around a laboratory scale biological reactor are presented     

The redox thermodynamics and kinetics of flavonoid rutin adsorbed at glassy carbon electrodes by stripping square wave voltammetry

The adsorptive accumulation of rutin (RU) at glassy carbon (GC) electrodes in 10% ethanol + 90% 1 mol dm⁻³ HClO₄ aqueous solution is studied by using cyclic (CV) and square wave (SWV) voltammetries. The Frumkin adsorption isotherm best described the specific interaction of rutin with carbon electrodes. By fitting the experimental data, values of −31.9 kJ mol⁻¹ and 0.54 ± 0.02 were obtained for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the surface redox process, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.644 ± 0.003 V and 0.44 ± 0.02 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 6.1 × 10² s⁻¹ was obtained. SWV was also employed to generate calibration curves. The lowest concentration of RU experimentally measured for a signal-to-noise ratio of 3:1 was 2 × 10⁻⁸ mol dm⁻³ (12 ppb).     

Designing a programmable analog signal conditioning circuit without loss of measurement range

Programmable analog signal conditioning circuits can be programmed in the field to permit their use in several applications with a variety of sensors with different output signal characteristics. The digital programming of the gain and dc level shift of a conditioning circuit can affect the measurement resolution and cause a reduction in the range of the measuring system in which it is employed. For a specified maximum acceptable loss in the measurement resolution, a procedure for defining and employing the programming values that guarantees the full measurement range is proposed. The proposed methodology takes into account practical implementation considerations and can be employed for designing either discrete or integrated circuits.     

Thermal-lens study of thermo-optical properties of tellurite glasses

Mode-mismatched Thermal Lens (TL) measurements were performed in 70TeO₂–19WO₃–7Na₂O–4Nb₂O₅ (% mol) tellurite glasses doped with either Er³⁺ or Tm³⁺ and co-doped with Er³⁺/Tm³⁺ ions. Thermo-optical parameters (D, K, ds/dQ and ds/dT) were obtained in function of thulium concentrations (0.39–1.6) × 10 ²⁰ ions/cm³. For Er³⁺/Tm³⁺ co-doped tellurite glasses, D and K values are practically independent of the Tm³⁺ concentrations used in this study. The average values of D and ds/dT obtained for tellurite glasses are: (3.1 ± 0.2) × 10⁻³ cm²/s and (16 ± 3) × 10⁻⁶ K⁻¹, respectively.