Linear polarization degree for detecting magnetic properties of small particles

Motivated by the recent advances with magnetic nanoparticles, in this research we propose a new technique for their characterization based on the measurement of certain polarimetric parameters of the scattered light, such as the linear polarization degree when it is determined at a "right-angle" scattering configuration. We will show the sensitivity of its spectral evolution with the magnetic properties of the particle.     

The effect of metal dispersion on the resonance of antennas at infrared frequencies

In this paper the optical parameters at infrared frequencies of metallic thin films were obtained experimentally using a variable angle spectroscopic ellipsometer and used to simulate numerically the frequency response of antennas and antenna-coupled detectors at infrared frequencies (5–15 μm). The simulation results agree with previously published data and practical guidelines are presented for the design and fabrication of dipole and bowtie antennas at infrared frequencies.     

Surface structure of liquid Li and Na: an ab initio molecular dynamics study

Molecular dynamics simulations of the liquid-vapor interfaces of liquid metals have been performed using first principles methods. Results are presented for liquid lithium and sodium near their respective triple points, for samples of 2000 particles in a slab geometry. The atomic density profiles show a pronounced stratification extending several atomic diameters into the bulk, which is similar to that already experimentally observed in liquid K, Ga, In, and Hg.     

Molecular multivalent electrolytes: microstructure and screening lengths

We study small rod-like molecular electrolytes solutions with their corresponding atomic counterions. The asymptotic length scales (decay length and wavelength) of the structural correlations are analyzed using the formalism of the dressed interaction site theory (DIST). The correlation functions are determined using the reference interaction site model equation complemented with a mixed approach in which the hypernetted-chain closure is used for the repulsive interactions, and the mean spherical approximation is used for the attractive interactions. The results from this scheme are in good agreement with the Monte Carlo computer simulations reported here. The asymptotic properties of the correlation functions of this molecular system are compared against those corresponding to two related simple (atomic) electrolyte models. The main conclusion is that the molecular structure of the ions lowers by two orders of magnitude the concentration at which the transition from monotonic to oscillatory decay occurs.     

Titanium dioxide doped with transition metals (MxTi1?xO2, M: Ni, Co): synthesis and characterization for its potential application as photoanode

This study presents the synthesis of TiO₂ doped with different amounts of Co and Ni, starting from a simple metallic titanium powder. A successful electrophoretic deposition of these materials on ITO electrodes was achieved for its potential application as photoanodes. EDX, diffuse reflectance UV–Vis spectroscopy, and XRD measurements gave information on the chemical composition of the material and the location of the Ni or Co within the crystal structure of TiO₂. Raman spectroscopy suggests that for a higher content of doping metal above a defined percentage, the formation of metal oxide is promoted. A preliminary study of photoelectrocatalytic orange dye degradation shows higher color removal efficiency as compared to the commercial TiO₂ material.     

Luminance adaptation model for increasing the dynamic range of an imaging system based on a CCD camera

We propose a luminance adaptation model (LAM) to increase the dynamic range of an imaging system when scenes containing areas of low and high illumination are imaged. The LAM that we developed is based on capturing images at different exposure times to obtain digital levels within the linear response zone for all the pixels in the image. The levels are subsequently transformed to a reference exposure time that is common to all pixels. We use a linear transformation whose coefficients are determined by the digital levels obtained for a set of flat-spectrum samples. In this study, the LAM is applied to a multispectral imaging system that is based on a CCD camera used for color measurements and spectral reconstructions. It is shown to be a very useful method for increasing the dynamic range of the system, whilst maintaining its accuracy.     

On the role of the colloidal stability of mesoporous silica nanoparticles as gene delivery vectors

Mesoporous silica nanoparticles have been synthesized and functionalized with four different types of molecules containing amino groups, i.e., with primary amines only, with quaternary amines, with quaternized cyclic amines, or with polyethylenimine (PEI), which is formed by primary, secondary, and tertiary amines. These nanoparticles were then incubated with reporter plasmids and the ability of the resulting complexes to transfect human cells was studied. Only nanoparticles functionalized with PEI were efficient for transfection. The agglomeration behavior and the electrokinetic potential of the nanoparticle–plasmid complexes have been studied, as well as their cell internalization behavior using a fluorescent-labeled plasmid that allows its monitorization by confocal microscopy. The results indicate that the efficiency of PEI-functionalized nanoparticles for transfection resides to some extent in the different characteristics imparted to the nanoparticles regarding agglomeration and surface charge behavior.     

Development of an optical refractometer by analysis of one-dimensional photonic bandgap structures with defects

A theoretical analysis of an optical fiber photonic-bandgap-based refractometer is presented. The design is based on a quarter-wave reflector with one defect. By modifying both the real and the imaginary parts of the index of refraction of the defects we begin to change either the frequency or the amplitude of the localized optical mode. So we could fabricate a specific optical fiber refractometer by combining all the variables: index of refractive index of the defects and the rest of layers, thickness of the defect, number of layers, etc. to yield a large set of design possibilities, for example, detecting wider or thinner ranges of refractive indices, or controlling the detection accuracy. Some rules for the practical implementation of the refractometer are given.