Instituto Politécnico Nacional

About: Instituto Politécnico Nacional is a education organization based out in Mexico City, Mexico. It is known for research contribution in the topics: Population & Context (language use). The organization has 43351 authors who have published 63315 publications receiving 938532 citations. The organization is also known as: Instituto Politécnico Nacional & Instituto Politecnico Nacional.

A behavioral biometric system based on human-computer interaction

Abstract: In this paper we describe a new behavioural biometric technique based on human computer interaction. We developed a system that captures the user interaction via a pointing device, and uses this behavioural information to verify the identity of an individual. Using statistical pattern recognition techniques, we developed a sequential classifier that processes user interaction, according to which the user identity is considered genuine if a predefined accuracy level is achieved, and the user is classified as an impostor otherwise. Two statistical models for the features were tested, namely Parzen density estimation and a unimodal distribution. The system was tested with different numbers of users in order to evaluate the scalability of the proposal. Experimental results show that the normal user interaction with the computer via a pointing device entails behavioural information with discriminating power, that can be explored for identity authentication.

Terahertz semiconductor-heterostructure lasers

Abstract: Injection lasers based on interminiband transitions in GaAs/AlGaAs heterostructures are operated in the THz range. Single-mode emission is achieved at 4.4THz, with output powers of 2.5mW and thresholds of few hundred A/cm/sup 2/ up to 50K.

Measurement of Cell Volume Changes by Fluorescence Self-Quenching

Abstract: At high concentrations, certain fluorophores undergo self-quenching, i.e., fluorescence intensity decreases with increasing fluorophore concentration. Accordingly, the self-quenching properties can be used for measuring water volume changes in lipid vesicles. In cells, quantitative determination of water transport using fluorescence self-quenching has been complicated by the requirement of relatively high (mM) and often toxic loading concentrations. Here we report a simple method that uses low (μM) loading concentrations of calcein-acetoxymethyl ester (calcein-AM) to obtain intracellular concentrations of the fluorophore calcein suitable for measurement of changes in cell water volume by self-quenching. The relationship between calcein fluorescence intensity, when excited at 490 nm (its excitation maximum), and calcein concentration was investigated in vitro and in various cultured cell types. The relationship was bell-shaped, with the negative slope in the concentration range where the fluorophore undergoes fluorescence self-quenching. In cultured retinal pigment epithelial cells, calcein fluorescence and extracellular osmolarity were linearly related. A 25-mOsm hypertonic challenge corresponded to a decrease in calcein fluorescence with high signal-to-noise ratio (>15). Similar results were obtained with the fluorophore BCECF when excited at its isosbestic wavelength (436 nm). The present results demonstrate the usefulness of fluorescence self-quenching to measure rapid changes in cell water volume.

Antioxidant effects of quercetin and catechin encapsulated into PLGA nanoparticles

Abstract: Polymeric nanoparticles (PLGA) have been developed for the encapsulation and controlled release of quercetin and catechin. Nanoparticles were fabricated using a solvent displacementmethod. Physicochemical properties were measured by light scattering, scanning electron microscopy and ζ-potential, X-ray diffraction, infrared spectroscopy and differential scanning calorimetry. Encapsulation efficiency and in vitro release profiles were obtained from differential pulse voltammetry experiments. Antioxidant properties of free and encapsulated flavonoids were determined by TBARS, fluorescence spectroscopy and standard chelating activity methods. Relatively small (d ≃ 400 nm) polymeric nanoparticles were obtained containing quercetin or catechin in a non-crystalline form (EE ≃ 79%) and the main interactions between the polymer and each flavonoid were found to consist of hydrogen bonds. In vitro release profiles were pH-dependant, the more acidic pH, the faster release of each flavonoid from the polymeric nanoparticles. The inhibition of the action of free radicals and chelating properties, were also enhanced when quercetin and catechin were encapsulated within PLGA nanoparticles. The information obtained from this study will facilitate the design and fabrication of polymeric nanoparticles as possible oral delivery systems for encapsulation, protection and controlled release of flavonoids aimed to prevent oxidative stress in human body or food products.