Marian Vlădescu

Studies on the Transient, Continuous and Pulsed Regimes of High Power LEDs

Monitoring the thermal regime of the high power LEDs used in lighting applications and in optical communications is nowadays a must. The paper presents our studies and experimental results concerning the transient, continuous and pulsed regimes of high power LEDs, based on a method for temperature measurement that makes use of the protection diode embedded in the LED package. The method proved to be consistent with the exponential law describing the transient regime and with the mathematical relation between continuous and pulsed regimes, qualifying thus as a potential monitoring tool for LED-based systems.

Quantitative Theory of Signal Inversion in RFID

Inversion is a phenomenon that affects the signal received by an RFID reader from a transponder in an unwanted way, as it creates zones of non-communication on the reader antenna. In a previous work we have shown how to locate and evaluate inversion with the aid of 2D maps produced with an automated scanner. The present paper supplements that work with a theory that clarifies the dependence of inversion on the parameters of the transponder circuit and on the magnetic coupling between antenna and transponder.

Optoelectronic Method for Determining the Aluminium Involved in Symptoms of Attention Deficit Hyperactivity Disorder Children

Aluminum is a chemical element atomic number 13. It is white-silver, insoluble in water under normal conditions. Despite its natural abundance, aluminum has no known biology function. It is a toxic residue, aluminum sulphate having an LD50 of 6207 mg/kg body, corresponding to 500 g per 80 kg person. Extremely acute toxicity without harm to health is of interest in view of the widespread occurrence of the element in the environment and in trade. Toxicity can be tracked after deposition into the bones and the central nervous system and is particularly high in patients with renal insufficiency. In very high doses, aluminum can cause neuro toxicity associated with altered function of the blood-brain barrier.

Key Aspects of Infrastructure-to-Vehicle Signaling Using Visible Light Communications

With the appearance of autonomous cars, an infrastructure-to-car communication system can be easily developed by using the visible light communication (VLC). The red and green lights play an important role in the safety of road traffic, being the most significate colors of the traffic light system. The role of the proposed system is to obtain automatic braking if the traffic lights are red and an audio warning in the case of yellow color by modulating the radiation emitted by the traffic light to transmit a code for each of red and yellow lights. A secondary solution is proposed which avoids the modification of the current infrastructure of the traffic light system by adding a supplementary light emission element. The element consists of an infrared emitter used to send either the red color code or the yellow color code depending on the illuminated traffic light.

Study on determining the photometric parameters for a white LED using a light meter

The paper presents the experiments performed in order to determine the most suitable measuring mode which could be used to notably increase the accuracy of the photometric parameters determination for a white LED using a light meter with multiple measurement modes for various classic light sources like tungsten (incandescent), fluorescent, mercury and sodium based. Light meters are used for measuring the illuminance, which is a photometric parameter and its determination is based on the properties of human sight sense. Knowing how the sensitivity of the eye varies with the wavelength, the spectral response of the sensor and the spectral composition of the radiation emitted by a certain light source, a correction curve can be applied over the sensed values and obtain an accurate measurement. Nowadays many light meters can contain multiple calibration curves for typical light sources, but not for LEDs, especially for white ones. Since multiple measurements can be done using each correction curve, the authors conducted experiments to determine how to combine the aforementioned results to obtain a good estimate for the illuminance of white LEDs.

Enhanced automated platform for 2D characterization of RFID communications

The characterization of the quality of communication between an RFID reader and a transponder at all expected positions of the latter on the reader antenna is of primal importance for the evaluation of performance of an RFID system. Continuing the line of instruments developed for this purpose by the authors, the present work proposes an enhanced version of a previously introduced automated platform for 2D evaluation. By featuring higher performance in terms of mechanical speed, the new version allows to obtain 2D maps of communication with a higher resolution that would have been prohibitive in terms of test duration with the previous version. The list of measurement procedures that can be executed with the platform is now enlarged with additional ones, such as the determination of the variation of the magnetic coupling between transponder and antenna across the antenna surface and the utilization of transponder simulators for evaluation of the quality of communication.

Method for the determination of cobalt from biological products with graphite furnace atomic absorption spectrometer

Cobalt is a chemical element with symbol Co and atomic number 27 and atomic weight 58.93. 59 Co is the only stable cobalt isotope and the only isotope to exist naturally on Earth. Cobalt is the active center of coenzymes called cobalamin or cyanocobalamin the most common example of which is vitamin B12. Vitamin B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system in the form of fatigue, depression and poor memory or even mania and psychosis. In order to study the degree of deficiency of the population with Co or the correctness of treatment with vitamin B12, a modern optoelectronic method for the determination of metals and metalloids from biological samples has been developed, Graphite Furnace – Atomic Absorption Spectrometer (GF– AAS) method is recommended. The technique is based on the fact that free atoms will absorb light at wavelengths characteristic of the element of interest. Free atoms of the chemical element can be produced from samples by the application of high temperatures. The system GF-AAS Varian used as biological samples, blood or urine that followed the digest of the organic matrix. For the investigations was used a high – performance GF-AAS with D2 – background correction system and a transversely heated graphite atomizer. As result of the use of the method are presented the concentration of Co in the blood or urine of a group of patient in Bucharest. The method is sensitive, reproducible relatively easy to apply, with a moderately costs.

Ionization pattern obtained in electrospray ionization or atmospheric pressure chemical ionization interfaces for authorized antidepressants in Romania

Antidepressants were found in 1950. In the 1990s there was a new generation of antidepressants. They act on the level of certain neurotransmitters extrasinpatic by its growth. After their mode of action antidepressants may be: SSRIs (Selective Serotonin Reuptake Inhibitors); (Serotonin-Norepinephrine Reuptake Inhibitors); SARIs (Serotonin Antagonist Reuptake Inhibitors); NRIs (Norepinephrine Reuptake Inhibitors); NDRIs (Norepinephrine-Dopamine Reuptake Inhibitors) NDRAs (Norepinephrine-Dopamine Releasing Agents); TCAs (Tricyclic Antidepressants); TeCAs (Tetracyclic Antidepressants); MAOIs (Monoamine Oxidase Inhibitors); agonist receptor 5-HT1A (5- hydroxytryptamine); antagonist receptor 5-HT2; SSREs (Selective Serotonin Reuptake Enhancers) and Sigma agonist receptor. To determine the presence of antidepressants in biological products, it has been used a system HPLC-MS (High Performance Liquid Chromatography – Mass Spectrometry) Varian 12001. The system is equipped with APCI (Atmospheric Pressure Chemical Ionization) or ESI (ElectroSpray Ionization) interface. To find antidepressants in unknown samples is necessary to recognize them after mass spectrum. Because the mass spectrum it is dependent on obtaining private parameters work of HPLC-MS system, and control interfaces, the mass spectra library was filled with the mass spectra of all approved antidepressants in Romania. The paper shows the mass spectra obtained in the HPLCMS system.

Optoelectronic method for determining platinum in biological products

Of all platinum metals, platinum has the most uses and it’s the most abundant and most easily to be processed. Its use in auto catalysts results in environmental contamination of crowded cities and high-traffic roads. In medicine, Pt is used as a cytostatic drug. In order to study the degree of contamination of the population with Pt or the correctness of treatment with Pt, it has been developed a method for its determination from urine or blood samples with a system Graphite Furnance - Atomic Absorption Spectrometer, (GF-AAS) Varian. There are presented the methods of sampling processing for blood or urine that followed the digest of the organic matrix. In the determination of the operating parameters for the system GF-AAS, was aimed the reducing of the nonanatomic absorbance by optimizing the drying temperatures, the calcination and atomization temperatures and the removal of the nonanatomic absorbance with D2 lamp. As a result of the use of the method are presented the concentrations of Pt in the blood or urine of a group of patients in Bucharest, a city with heavy traffic of vehicles. GF-AAS method presented is sensitive, reproducible, and relatively easy to apply with an acceptable cost. With this method, the concentration of Pt can be determined from blood and urine, both in order to establish the degree of contamination with Pt and for monitoring cancer therapy with platinum compounds.

Parameter extraction of an organic solar cell using asymptotic estimation and Lambert W function

A theoretical characterization of an organic solar cell has been realized based on its equivalent model and an I-V curve corresponding to ITO/PEDOT/MEH-PPV:PCBM(1:4)/LiF/Al cell, taken from the literature. The parameters of the equivalent model have been determined using two methods: the approximation method and the Lambert W function. For the considered curve, the parameter values that have been obtained are similar to the results presented in literature. It has also been shown that the Lambert W function presents a considerably smaller error compared to the approximation method.