Determination of ascorbic acid by perturbation of the oscillation pattern of the Belousov-Zhabotinskii reaction using a continuous flow system

Propõe-se a determinação potenciométrica de ácido ascórbico (vitamina C) em medicamentos, em um sistema em fluxo, utilizando-se como princípio o efeito desta substância no padrão de oscilação da reação de Belousov-Zhabotinskii. Esta reação envolve a oxidação de um composto orgânico, como o ácido malônico, por íons bromato em meio de ácido sulfúrico, com o íon cério (IV) usado como catalisador. Tanto a frequência como a amplitude das oscilações podem ser usadas como parâmetros analíticos. O ácido ascórbico pode promover a diminuição da diferença de potencial, aumentando a amplitude na reação de Belousov-Zhabotinskii quando esta substância é injetada no meio reacional. O sistema químico é perturbado com quantidades variáveis de ácido ascórbico, o que resulta em um aumento da amplitude que é linearmente proporcional à concentração de ácido ascórbico. A maioria dos íons comumente encontrados em amostras de medicamentos não interfere na determinação. As condições experimentais foram escolhidas através de um planejamento fatorial 24, onde as concentrações dos reagentes bromato de potássio, sulfato de cério (IV), ácido malônico e ácido sulfúrico foram as variáveis estudadas. A metodologia para a determinação de ácido ascórbico resultou em um procedimento relativamente simples, com limite de detecção de 1,63 x 10-4 mol L-1. Na determinação de ácido ascórbico em amostras de medicamentos obteve-se resultados em concordância com os valores declarados pelos fabricantes. O método desenvolvido apresenta-se como uma alternativa para a determinação de ácido ascórbico em medicamentos, pois o procedimento é relativamente simples e de baixo custo.

Determination of ascorbic acid by perturbation of the oscillation pattern of the Belousov-Zhabotinskii reaction using a continuous flow system

Propõe-se a determinação potenciométrica de ácido ascórbico (vitamina C) em medicamentos, em um sistema em fluxo, utilizando-se como princípio o efeito desta substância no padrão de oscilação da reação de Belousov-Zhabotinskii. Esta reação envolve a oxidação de um composto orgânico, como o ácido malônico, por íons bromato em meio de ácido sulfúrico, com o íon cério (IV) usado como catalisador. Tanto a frequência como a amplitude das oscilações podem ser usadas como parâmetros analíticos. O ácido ascórbico pode promover a diminuição da diferença de potencial, aumentando a amplitude na reação de Belousov-Zhabotinskii quando esta substância é injetada no meio reacional. O sistema químico é perturbado com quantidades variáveis de ácido ascórbico, o que resulta em um aumento da amplitude que é linearmente proporcional à concentração de ácido ascórbico. A maioria dos íons comumente encontrados em amostras de medicamentos não interfere na determinação. As condições experimentais foram escolhidas através de um planejamento fatorial 24, onde as concentrações dos reagentes bromato de potássio, sulfato de cério (IV), ácido malônico e ácido sulfúrico foram as variáveis estudadas. A metodologia para a determinação de ácido ascórbico resultou em um procedimento relativamente simples, com limite de detecção de 1,63 x 10-4 mol L-1. Na determinação de ácido ascórbico em amostras de medicamentos obteve-se resultados em concordância com os valores declarados pelos fabricantes. O método desenvolvido apresenta-se como uma alternativa para a determinação de ácido ascórbico em medicamentos, pois o procedimento é relativamente simples e de baixo custo.

Novel Method for Surface Tension Measurement: the Drop-Bounce Method

The surface tension of liquids at high temperatures is generally measured with the well-established oscillating drop method in a contactless environment. However, technical difficulties in surface tension measurements make it hard to apply the oscillating drop method to the aerodynamic levitation (ADL) system, the most reliable levitation technique for liquids with low electrical conductivity. In this study, we developed a novel drop–bounce method that can be used within an ADL system to measure the surface tension of liquids. A levitated molten sample was first dropped onto an inert substrate through a splittable nozzle. The rebounded sample’s oscillatory motion behaved as it would under microgravity conditions during its free-fall, and oscillations were obtained only in the l=2, m=0 mode. Fourier transformation of the oscillation pattern provided resonant frequency of the l=2, m=0 mode and enabled the calculation of the surface tension of the sample under knowledge of its mass. Furthermore, a short experimental duration of less than 50 ms significantly reduced the possibility of surface evaporation in the sample. Our measured surface tension data from 1354 K to 1827 K for gold exhibited a standard deviation of 13.4 mJ/m2 and were consistent with the data published by Egry et al. under microgravity conditions, with a maximum deviation of 1.5% between the two fitted linear equations.

Dynamic expression of a HR neuron model under an electric field

The movement of large amounts of ions (e.g., potassium, sodium and calcium) in the nervous system triggers time-varying electromagnetic fields that further regulate the firing activity of neurons. Accordingly, the discharge states of a modified Hindmarsh–Rose (HR) neuron model under an electric field are studied by numerical simulation. By using the Matcont software package and its programming, the global basins of attraction for the model are analyzed, and it is found that the model has a coexistence oscillation pattern and hidden discharge behavior caused by subcritical Hopf bifurcation. Furthermore, the model’s unstable branches are effectively controlled based on the Washout controller and eliminating the hidden discharge states. Interestingly, by analyzing the two-parametric bifurcation analysis, we also find that the model generally has a comb-shaped chaotic structure and a periodic-adding bifurcation pattern. Additionally, considering that the electric field is inevitably disturbed periodically, the discharge states of this model are more complex and have abundant coexisting oscillation modes. The research results will provide a useful reference for understanding the complex dynamic characteristics of neurons under an electric field.

Vocal fold oscillation pattern changes related to loudness in patients with vocal fold mass lesions

Introduction Vocal fold mass lesions can affect vocal fold oscillation patterns and therefore voice production. It has been previously observed that perturbation values from audio signals were lower with increased loudness. However, how much the oscillation patterns change with gradual alteration of loudness is not yet fully understood. Material and methods Eight patients with vocal fold mass lesions were asked to perform a glide from minimum to maximum loudness on the vowel /i/, ƒo of 125 Hz for male or 250 Hz for female voices. During phonation the subjects were simultaneously recorded with transnasal high speed videoendoscopy (HSV, 20,000 fps), electroglottography (EGG), and an audio recording. Based on the HSV material the Glottal Area Waveform (GAW) was segmented and GAW parameters were computed. Results The greatest vocal fold irregularities were observed at different values between minimum and maximum sound pressure level. There was a relevant discrepancy between the HSV and EGG derived open quotients. Furthermore, the EGG derived sample entropy and GAW values also evidenced different behavior. Conclusions The amount of vocal fold irregularity changes with varying loudness. Therefore, any evaluation of the voice should be performed under different loudness conditions. The discrepancy between EGG and GAW values appears to be much stronger in patients with vocal fold mass lesions than those with normal physiological conditions. Level of evidence 4.

An Extraordinary Winter in the Polar North

An exceptionally strong stratospheric polar vortex coincided with a record-breaking Arctic Oscillation pattern and ozone destruction during the 2019–2020 winter season.

Influence of the beam oscillation pattern and oscillation frequency on the temperature field in laser brazing with keyhole formation

Laser keyhole brazing is an opportunity to increase the process efficiency in laser brazing processes. Using small spot sizes increases the intensity and leads to the formation of a vapour capillary (keyhole) in the brazing material when a material-specific threshold value is exceeded. Due to multiple reflections/absorptions of the laser beam in the keyhole, the process efficiency increases in comparison with conventional brazing processes with single Fresnel absorption on the surface, especially when using high-reflectivity braze materials, such as aluminium-based or copper-based alloys. The energy must be distributed adequately by applying beam oscillation transversal to the brazing direction. In laser brazing processes, the temperature field in the interface between brazing and substrate material is a major factor. To analyse the effect of beam oscillation, it is assumed in this study that the temperature distribution at the surface of the melt pool is a suitable approximation for the temperature distribution at the interface to the substrate. Two key parameters are defined to quantify the temperature field referring to the homogeneity: the temporal local temperature-time curve and the temperature distribution transverse to the brazing direction. While the oscillation frequency influences the first mentioned parameter by decreasing the time interval between the local laser passes, the oscillation pattern affects the second parameter by adjusting the local actual beam velocity and its consistency.

Micromachined Rate-Integrating Gyroscopes: Concept, Asymmetry Error Sources and Phenomena

Rate-integrating gyroscope (RIG) operation is an attractive operation scheme for micro gyroscopes, because it can provide direct angle measurement and a high dynamic range. However, its zero rate output (ZRO) has a severe drift issue. This work compared the difference between rate and rate-integrating gyroscope operations, and further modeled the gyroscope with asymmetric error terms. Then the influences of these non-ideal factors were analyzed to abridge the ZRO drift phenomena and the sources. The numerical verification proved the theory that such an oscillation pattern is caused by the stiffness mismatch, and decaying to X/Y axis manner resulted from the damping errors. The conclusions can contribute to aiding engineers to rapidly locate the bottlenecks of RIG operations.