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Brain-machine interfaces (BMIs) are useful tools for controlling assistive devices. One current approach in this field is continuous trajectory reconstruction (CTR), which decodes variables from electroencephalographic (EEG) signals. In this study, the CTR approach was applied to estimate kinetic variables from lower limb joints during pre-gait movements. The methodology consisted of a multi-layer perceptron capable of detecting patterns that represent the relation between EEG and torque signals acquired during motion tasks. The study also searched for an optimal subset of EEG channels based on the resulting patterns. A group of volunteers was recruited to execute pre-gait movements with both lower limbs to test the methodology. Results show that decodings of extracted patterns were successful in terms of the selected performance metrics; that is, the coefficient of determination, correlation coefficient, and signal-to-noise ratio. These metrics suggest that decodings for the right lower limb are better than for the left one, and that the most frequent electrodes in the optimal subsets for each task and joint show a tendency to lateralize. The results obtained suggest that this machine learning scheme could be used for future studies of the CTR of kinetic variables.

Rather than focusing on a focal spot, aberrated wavefields spread out over a region. As a wave phenomenon, optical aberrations are analyzed in terms of waves propagating in the 3D space. In this work, we report the observation of 2D longitudinal aberrated wavefields. This observation can be visualized by mapping the intensity distributions of surface plasmon polaritons (SPPs) that propagate on a metal/air interface using leakage radiation microscopy. The orientation of the SPP beam is tweaked by tilting and translating the system to mimic aberrated beams, presenting known Seidel terms: defocus, spherical, coma, and tilt aberration. This approach allows the examination of the longitudinal evolution of aberrated beams in a visual and rapid manner, in contrast to more complicated post-processing reconstructions.

Ray tracing in gradient-index (GRIN) media has been traditionally performed either by using the analytical or numerical solutions to the Eikonal equation or by creating a layered medium where Snell’s law is calculated in each layer. In this paper, an exact general method to perform ray tracing in GRIN media is presented based on the invariants of the system as stated by Fermat’s principle when the media presents symmetries. Its advantage, compared with other methods reported in the literature, relies on its easy implementation. Besides the GRIN distribution and the initial conditions of the incident ray, once the invariants of the system are stated the resulting math is simple to solve and interpret. To benchmark the algorithm, ray tracing in typical cases of GRIN media is calculated, finding minimal discrepancies between the analytical solutions and our simulations. The used media are axial refractive index and parabolic index fiber and lenses with spherical gradient-index symmetry, such as: Luneburg’s, Gutman’s, generalized Maxwell’s Fish-eye, Eaton’s, and concentrator lenses. Our method can be further applied to distributions with symmetries associated with other common curvilinear orthogonal coordinate systems, in particular to those associated to the separability of the Helmholtz equation that would allow us to investigate wave optics in these GRIN media with the associated geometries.

To the best of our knowledge, at the present time there is no answer to the fundamental question stated in the title that provides a complete and satisfactory physical description of the structured nature of Hermite-Gauss beams. The purpose of this manuscript is to provide proper answers supported by a rigorous mathematical-physics framework that is physically consistent with the observed propagation of these beams under different circumstances. In the process we identify that the paraxial approximation introduces spurious effects in the solutions that are unphysical. By removing them and using the property of self-healing, that is characteristic to structured beams, we demonstrate that Hermite-Gaussian beams are constituted by the superposition of four traveling waves.

In the description of physical systems it is common to discard singular solutions to second order differential equations due to their apparent lack of physical meaning. Nevertheless, it has been demonstrated, using a mathematical-physics approach, that singular solutions can be used in the description of optical beams. In this paper, we construct and study paraxial traveling-waves using the full set of solutions to the paraxial wave equation, and prove that they diverge at infinity. We ascribe that non-physical effect to the paraxial approximation of the Helmholtz equation. Despite this, we show that these traveling waves provide a mathematical-physics framework that unveils orbital angular momentum carrying Laguerre–Gauss beam as the superposition of these traveling waves, and permits a physical description of the self-healing process.

In this work, we study the magnetoelastic behavior of ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}$ ($0.11lxl0.19$) thin films, grown on glass and oxidized Si(100) amorphous substrates, that present an isotropic crystalline texture in the film plane. The magnetoelastic coupling coefficients are obtained through the cantilever deflection technique. We find that the magnetoelastic response is larger for samples grown on glass with respect to those grown on Si(100), and such a response increases for larger Ga concentrations for both substrates used. Furthermore, the increasing substrate temperature during growth does not appear to have a significant effect on magnetoelastic behavior of samples grown on Si(100). From a model that takes into account the elastic grain interaction for isotropic systems, we are able to describe the experimentally observed behavior. We find that the magnetoelastic response of the samples grown on glass are well described by the Voigt model, while the samples on Si(100) present an intermediate response between the Voigt and Reuss models.

Crassostrea virginica was exposed to different light crude oil levels to assess the effect on transcriptomic response and metabolic rate. The exposure time was 21 days, and levels of 100 and 200 μg/L were used, including a control. The most significant difference among treatments was the overexpression of several genes associated with energy production, reactive oxygen species (ROS) regulation, immune system response, and inflammatory response. Also, a hydrocarbon concentration-related pattern was identified in ROS regulation, with a gene expression ratio near 1.8:1 between 200 and 100 μg/L treatments. Statistical analysis showed no interaction effect for metabolic rate; however, significant differences were found for oil concentration and time factors, with a higher oxygen consumption at 200 μg/L. Our findings provide novel information about the metabolic response of C. virginica during hydrocarbons exposure. In addition, our results point out which biological processes should be investigated as targets for searching bioindicators.

A system based on the use of two artificial neural networks (ANNs) to determine the location of the scleral spur of the human eye in ocular images generated by an ultrasound biomicroscopy is presented in this paper. The two ANNs establish a relationship between the distance of four manually placed landmarks in an ocular image with the coordinates of the scleral spur. The latter coordinates are generated by the expert knowledge of a subject matter specialist. Trained ANNs that generate good results for scleral spur location are incorporated into a software system. Statistical indicators and results yield an efficiency performance above 95%.

In the seminal paper on elegant Gaussian beams, Siegman introduced them as a complex-argument variant of standard Gaussian beams and proved that they cannot be eigenmodes of spherical resonators. In this work, we demonstrate that this intrinsic asymmetry can be overcome by judiciously superposing a finite number of elegant Laguerre–Gauss beams, all of them having the same amount of orbital angular momentum. In other words, we found a new family of elegant modes that are eigenmodes of confocal resonators and will call them Siegman’s elegant resonator modes.

In this work, we present a systematic study on the relation between the elastic behavior and the structural properties of polycrystalline Fe0.89Ga0.11 thin films deposited on Si(100) substrates. By carrying out pole figure (PF) measurements, we determined the evolution of the texture components, residual stress and Young's modulus (Ys) as a function of the Ar pressure. The samples display several fiber-like texture components (where the fiber axes is always along the growth direction) beside to a random component; the texture component weights depend on the Ar pressure. The study of the residual stress reveals that the samples present a tensile stress, that relaxes when the Ar pressure increases. In the case of Ys, the estimated values vary slightly within the Ar pressure range studied. Finally, the residual stress and Ys behavior is correlated with the microstructure evolution by using the orientation distribution function (ODF) simulated from the PFs.

In recent work, we showed how the optical response of the human eye’s crystalline lens can be modeled using a single function. We believe that this development will inform designs for applications such as intraocular implant lenses, and that it also has wider potential applications in areas including biomedical optics, ophthalmology and engineering.

It is well known that optics and classical mechanics are intimately related. One of the most important concepts in classical mechanics is that of a particle in a central potential that leads to the Newtonian description of the planetary dynamics. Within this, a relevant result is Kepler’s second law that is related to the conservation of orbital angular momentum, one of the fundamental laws in physics. In this paper, we demonstrate that it is possible to find the conditions that allow us to state Kepler’s second law for optical beams with orbital angular momentum by analyzing the streamlines of their energy flow. We find that the optical Kepler’s law is satisfied only for cylindrical symmetric beams in contrast to the classical mechanics situation that is satisfied for the other conic geometries, namely, parabolic, elliptical and hyperbolic. We propose a novel approach to confirm our analytic results: we observe the propagation of the Arago’s spot created by a beam with orbital angular momentum as a local “light-tracer” instead of looking at the propagation of the whole beam. The observed patterns fully agree with the prediction of our formalism.

The lens is a complex optical component of the human eye because of its physiological structure: the surface is aspherical and the structural entities create a gradient refractive index (GRIN). Most existent models of the lens deal with its external shape independently of the refractive index and, subsequently, through optimization processes, adjust the imaging properties. In this paper, we propose a physiologically realistic GRIN model of the lens based on a single function for the whole lens that accurately describes different accommodative states simultaneously providing the corresponding refractive index distribution and the external shape of the lens by changing a single parameter that we associate with the function of the ciliary body. This simple, but highly accurate model, is incorporated into a schematic eye constructed with reported experimental biometric data and accommodation is simulated over a range of 0 to 6 diopters to select the optimum levels of image quality. Changes with accommodation in equatorial and total axial lens thicknesses, as well as aberrations, are found to lie within reported biometric data ranges.

When a circular aperture is uniformly illuminated, it is possible to observe in the far field an image of a bright circle surrounded by faint rings known as the Airy pattern or Airy disk. This pattern is described by the first-order Bessel function of the first type divided by its argument expressed in circular coordinates. We introduce the higher-order Bessel functions with a vortex azimuthal factor to propose a family of functions to generalize the function defining the Airy pattern. These functions, which we call vortex Jinc functions, happen to form an orthogonal set. We use this property to investigate their usefulness in fitting various surfaces in a circular domain, with applications in precision optical manufacturing, wavefront optics, and visual optics, among others. We compare them with other well-known sets of orthogonal functions, and our findings show that they are suitable for these tasks and can pose an advantage when dealing with surfaces that concentrate a considerable amount of their information near the center of a circular domain, making them suitable applications in visual optics or analysis of aberrations of optical systems, for instance, to analyze the point spread function.

We present new families of vortex beams with orbital angular momentum establishing a generalization of the Laguerre-Gauss beams in its standard and elegant formulation. Their closed analytical free-space propagation formula is obtained.

In this Letter, a Gabor superlens with variable focus is presented. This configuration uses tunable liquid lenses in the third microlens array of the Gabor superlens. By applying voltage, the radius of curvature of the micro-tunable doublet arrays changes, and the Gabor conditions are fulfilled at different focal planes. As a consequence, the magnification of the image at the focal planes changes, and a zoom effect is observed. The marginal depth plane for this system goes from 0.86 to 0.89 mm. The optical simulation, calculations, and results of the simulated optical system performance are presented.

By means of numerical simulations we provide proof of concept for a low cost cone locating system whose function is based on vortex beams. The system described here does not lose precision compared to commercial standards. We investigate the advantages of imaging individual cones using vortex phase masks of different topological charge. We provide numerical simulations of two different setups that are combined to take advantage of optical vortices for two purposes: (a) resolve pairs of cones within the photoreceptor mosaic, and (b) to pinpoint positions of unresolved cones, we study the stability of this configuration against basic wavefront aberrations. The combination of setups can perform detection and positioning tasks with no correction for aberrations required. We show a simulation of how the system would produce a map of retinal cones.

In the present work, the production of bioemulsifier (BE) by a lactic acid bacterium (LAB) grown at 25 °C in lacticwhey-based media for 24 h was evaluated. Maximum production was detected in a medium containing yeastextract, peptone and lactic whey (LAPLW medium), with a yield of 270 mg L−1. The BE proved to be moreinnocuous for Caco-2 cells, used as a toxicological indicator, than the non-ionic surfactant Triton X-100. Inaddition, the microbial product presented higher stability to changes in temperature (37 °C to 100 °C), pH(2?10), and salt concentration (5% and 20%, w/v) than the synthetic surfactant. Regarding emulsifying capacitytested against different hydrophobic substrates (kerosene, motor oil, diesel, sunflower oil, and grape oil), the BEdisplayed E24 values similar to or even better than those of Triton X-100. Finally, Triton X-100 caused irreversible modifications on the giant unilamellar vesicles (used as model membrane system), promoting the solubilization of the lipid bilayers. Nevertheless, BE induced temporary modifications of the membrane, which isassociated with incorporation of the bioproduct in the outer layer. These results demonstrate the role of BE inbiological processes, including reversible changes in microbial membranes to enhance the access to hydrophobicsubstrates. Fil: Gianni de Carvalho, Katia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina Fil: Gómez, Johana E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina Fil: Vallejo, Marisol. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Trelew; Argentina Fil: Marguet, Emilio Rogelio. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Trelew; Argentina Fil: Perotti, Nora Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina Fil: Donato, Maressa. Universidade de Sao Paulo; Brasil Fil: Itri, Rosangela. Universidade de Sao Paulo; Brasil Fil: Colin, Veronica Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina

We present a new design of a plasmonic Luneburg lens made from a gradient-index metasurface that was constructed with an array of nanometer-sized holes in a dielectric thin film. The fabricated structure consists of a planar lens with a diameter of 8.7 μm composed of a rectangular array of holes with a periodicity of 300 nm. The experimental characterization includes leakage-radiation microscopy imaging in the direction and frequency space. The former allows for characterization of the point spread function and phase distribution, whereas the latter grants access to qualitative measurements of the effective mode indices inside the plasmonic lens. The experimental results presented here are in good agreement with the expected average performance predicted by the numerical calculations. Nevertheless, the robustness of the characterization techniques presented here is also exploited to determine deviations from the design parameters.

Purpose We propose the Bessel Circular Functions as alternatives of the Zernike Circle Polynomials to represent relevant circular ophthalmic surfaces. Methods We assess the fitting capabilities of the orthogonal Bessel Circular Functions by comparing them to Zernike Circle Polynomials for approximating a variety of computationally generated surfaces which can represent ophthalmic surfaces. Results The Bessel Circular Functions showed better modelling capabilities for surfaces with abrupt variations such as the anterior eye surface at the limbus region, and influence functions. From our studies we find that the Bessel Circular Functions can be more suitable for studying particular features of post surgical corneal surfaces. Conclusions We show that given their boundary conditions and free oscillating properties, the Bessel Circular Functions are an alternative for representing specific wavefronts and can be better than the Zernike Circle Polynomials for some important cases of corneal surfaces, influence functions and the complete anterior corneal surface.

In this paper we demonstrate that using a mathematical physics approach (focusing the attention to the physics and using mathematics as a tool) it is possible to visualize the formation of the transverse modes inside a cylindrical waveguide. In opposition, the physical mathematics solutions (looking at the mathematical problem and then trying to impose a physical interpretation), when studying cylindrical waveguides yields to the Bessel differential equation and then it is argued that in the core are only the Bessel functions of the first kind those who describe the transverse modes. And the Neumann functions are deemed non physical due to its singularity at the origin and eliminated from the final description of the solution. In this paper we show, using a geometrical-wave optics approach, that the inclusion of this function is physically necessary to describe fully and properly the formation of the propagating transverse modes. Also, the field in the outside of a dielectric waveguide arises in a natural way.

Ray tracing in spherical Luneburg lenses has always been represented in 2D. All propagation planes in a 3D spherical Luneburg lens generate the same ray tracing, due to its radial symmetry. A geometry without radial symmetry generates a different ray tracing. For this reason, a new ray tracing method in 3D through spherical and elliptical Luneburg lenses using 2D methods is proposed. The physics of the propagation is shown here, which allows us to make a ray tracing associated with a vortex beam. A 3D ray tracing in a composite modified Luneburg lens that represents the human eye lens is also presented.

ATR–FTIR has been used together with principal components analysis to study some reference strains belonging to five different Candida species and 20 Candida albicans isolates from three HIV + patients under different fluconazole regimens. The five reference strains were easily differentiated by using first derivative spectra of the carbohydrate region comprising the spectral range 900–1200 cm −1 . For the C. albicans clinical isolates, classification obtained by Fourier-transform infrared (FTIR) spectroscopy was compared with data from the genotypic method, PFGE. Results show a good correlation between the two methods for one patient who presented a partially conserved immune system with no previous fluconazole treatment, where all C. albicans strains isolated were susceptible to this antifungal agent. Divergences in the two methods appear for the two immuno-compromised patients receiving long-term fluconazole treatment. It is very probable that such iterative antifungal treatment can cause strong alterations in the yeast cell wall membrane and that the mismatch of the two techniques highlights the complex situation of strain-level identification and differentiation of clinical isolates originating from patients under prolonged treatment.

In this article, we develop a novel indirect second kind integral equation formulation for the solution of the mixed boundary value problem for Stokes flow between two closed surfaces (multiple-connected domain). At the exterior surface the fluid velocity is specified (boundary condition of the first kind) and at the interior surface the fluid surface traction is given (boundary condition of the second kind). The theoretical background to the proposed technique is explained in detail, including mathematical proofs of existence and uniqueness of solution. Numerical results of test examples are included to validate the formulation. As expected, the numerical solution of the proposed approach is very stable under iterative solvers requiring few numbers of iteration to achieve a desirable accuracy, even for very large number of surface nodes. Copyright © 2001 John Wiley & Sons, Ltd.

A multipolar expansion technique is applied to the indirect formulation of the boundary element method in order to solve the two-dimensional internal Stokes flow second kind boundary value problems. The algorithm is based on a multipolar expansion for the far field and numerical evaluation for the near field. Due to the nature of the algorithm, it is necessary to resort to the use of an iterative solver for the resulting algebraic linear system of equations. A parallel implementation is designed to take advantage of the natural domain decomposition of fast multipolar techniques and bring further improvements. Copyright © 2000 John Wiley & Sons, Ltd.

The ability to control the spin current injection has been explored on a hybrid magnetoelectric system consisting of a (011)-cut ferroelectric lead magnesium niobate-lead titanate (PMNT) single crystal, a ferromagnetic FePt alloy, and a metallic Pt. With this PMNT/FePt/Pt structure we have been able to control the magnetic field position or the microwave excitation frequency at which the spin pumping phenomenon between FePt and Pt occurs. We demonstrate that the magnetoelectric heterostructure operating in the L-T (longitudinal magnetized-transverse polarized) mode couples the PMNT crystal to the magnetostrictive FePt/Pt bilayer, displaying a strong magnetoelectric coefficient of ∼140 Oe cm kV-1. Our results show that this mechanism can be effectively exploited as a tunable spin current intensity emitter and open the possibility to create an oscillating or a bistable switch to effectively manipulate spin currents. Fil: Gomez, Javier Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina Fil: Vargas, Jose Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina Fil: Aviles Felix, Luis Steven. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina Fil: Butera, Alejandro Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina

Multi-aperture optics based on insects and arthropods eyes, is an interesting topic related to the development of miniaturized non-conventional optical designs. This novel concept has been used in image formation devices that offer many benefits in miniaturization and in improving certain optical characteristics, like a widef field of view. Energy concentration presents a good application for this technology. We show here, the description of the propagation of multiple laser beams through an ultra-thin objective lens that consists of a series of microlens arrays, and the fact that they have a common focal point, give us the option to achieve a high power concentration that results in the addition of the multiple lasers intensity. Lens configuration, equations, propagation, and optical performance are described.

A new lens model based on the gradient-index Luneburg lens and composed of two oblate half spheroids of different curvatures is presented. The spherically symmetric Luneburg lens is modified to create continuous isoindicial contours and to incorporate curvatures that are similar to those found in a human lens. The imaging capabilities of the model and the changes in the gradient index profile are tested for five object distances, for a fixed geometry and for a fixed image distance. The central refractive index decreases with decreasing object distance. This indicates that in order to focus at the same image distance as is required in the eye, a decrease in refractive power is needed for rays from closer objects that meet the lens surface at steeper angles compared to rays from more distant objects. This ensures a highly focused image with no spherical aberration.

Differentiation of Candida species resides on biochemical reactions and morphological features. However, phenotypic variations within some species such as Candida albicans has led to confusion in taxonomical and clinical classification of Candida species. Recent developments in analytical instrumentation and statistical methods, have enabled Fourier Transform Infrared Spectroscopy (FTIR) to emerge as a rapid, accurate and inexpensive method to characterize microorganisms [1–3]. The aim of present study is to characterize 5 reference strains of Candida species (C. albicans, C. parapsilosis, C. knisei, C. glabrata and C. tropicalis) using attenuated total-reflectance (ATR)- FTIR spectroscopy, i.e., without any preparation of the yeast colonies. These results could in turn be used to construct a data base for comparison of clinical strains.

In order to study polymorphisms of the DNA insertion sequence 6110 (IS6110) in Mycobacterium tuberculosis strains isolated from Colombian patients, together with resistance to antituberculous medications in the Department of Quindío, Colombia, a prospective study was conducted using a consecutive sample of 59 patients with symptomatic pulmonary tuberculosis whose cases had been confirmed by bacilloscopy, both with and without a history of treatment. The patients, who were participating in the Tuberculosis Control Program of the Regional Health Institute of Quindío in Armenia, included all individuals attending local health centers and hospitals between March and July 1993 who were referred to the regional institute. Sputum specimens from each patient were cultured and subjected to drug sensitivity tests. Subsequently, restriction fragment length polymorphisms (RFLP) of IS6110 from 27 patients were analyzed. The patients' treatment histories were used to classify their cases according to WHO criteria. Forty-five cultures were found positive, 44 for M. tuberculosis and 1 for M. africanum. Initial drug resistance was observed in 4 of 42 new cases, or 9.5% (95% CI: 0.6, 18), 2 showing resistance to isoniazid (INH) and 2 to isoniazid plus streptomycin (INH-SM). Acquired resistance was observed in 2 of the 3 chronic cases and relapses, the bacteria being resistant to isoniazid, rifampicin, and streptomycin (INH-RM-SM) in one case and to isoniazid, ethambutol, rifampicin, and streptomycin (INH-EMB-RM-SM) in the other. In those 27 strains subjected to RFLP analysis, the number of copies of IS6110 ranged from 6 to 17. Similarity coefficients revealed five distinct groups of strains. Overall, the RFLP analysis permitted most of the strains to be distinguished from one another, implying that the polymorphisms involved are sufficient to permit effective employment of this technique, which appears to have considerable potential for use in epidemiologic studies and in work designed to provide a basis for tuberculosis control program decision-making.

The purpose of this study was to determine the polymorphism of insertion segment 6110 (IS6110) in strains of Mycobacterium tuberculosis isolated from Colombian patients as well as the current status of resistance to antituberculosis drugs in the department of Quindío, Colombia. To this end, a prospective study was performed with a consecutive sample of 59 patients who sought care at local health centers and hospitals in rural and urban areas of Quindío from March to July 1993. The patients in the sample had symptomatic pulmonary tuberculosis confirmed by bacteriologic inspection of sputum, with and without a history of treatment, and were participants in the Tuberculosis Control Program of the Sectional Health Institute of Quindío in Armenia, Colombia. Sputum cultures and drug sensitivity tests were done. Later, restriction fragment length polymorphisms (RFLP) of IS6110 were analyzed in accordance with the protocols of van Soolingen et al. (1992). Cases were classified by treatment history, applying the criteria of WHO (1991). The results showed 44 cultures positive for M. tuberculosis and one positive for M. africanum. Primary drug resistance was found in 4 of 42 cultures, or 9.5% (CI 95%: 0.6 to 18); 4.8% were resistant to isoniazid (INH) and 4.8% to isoniazid and streptomycin (INH-SM). Acquired resistance was found in two of three cultures, or 66% (to isoniazid, rifampicin, and streptomycin [INH-RM-SM] and to isoniazid, ethambutol, rifampicin, and streptomycin [INH-EMB-RM-SM]). In 27 strains submitted to RFLP analysis, the number of copies of IS6110 varied from 6 to 17. Similarity coefficients revealed five distinct groups.(ABSTRACT TRUNCATED AT 250 WORDS)

We have developed an alternative method for building up a nanogranular system and have analysed its magnetic properties. Using a chemical route we have obtained magnetite nanoparticles with an average diameter of 4.5?nm and with a very narrow size distribution (??20%). These particles have been studied dispersed in a polymer, in powder form, and embedded in a permalloy ferromagnetic matrix which was deposited by sputtering techniques. DC magnetization and electron spin resonance were employed for analysing the magnetic response in these samples, showing a very good agreement with the structural characterization. The thermal stability has been probed in the three systems and the magnetic measurements allowed us to estimate a threefold increase in the energy barrier when the particles are immersed in a ferromagnetic host.