Scielo RSS <![CDATA[Revista mexicana de física]]> http://www.scielo.org.mx/rss.php?pid=0035-001X20160003&lang=en vol. 62 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.mx/img/en/fbpelogp.gif http://www.scielo.org.mx <![CDATA[Colloids and composite materials Au/PVP and Ag/PVP generated by laser ablation in polymeric liquid environment]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300188&lng=en&nrm=iso&tlng=en Abstract Pulsed laser ablation of Silver and Gold targets, immersed in a polymeric solution of Polyvinylpyrrolidone (PVP), is used to generate colloids and composite metal-polymer. Solutions of PVP in deionized water at different concentrations are employed. Two PVP number average molecular weights were considered, 10000 g/mol and 55000 g/mol. The high purity targets are irradiated between 20 min and40 min with the third harmonic (THG) ( λ = 335 nm) of a Nd:YAG laser operating at a rate of 10 Hz with pulses of 8 ns. Optical spectroscopy in UV and vis regions, Scanning Electron Microscopy (SEM), High Resolution Scanning Electron Microscopy (HR-SEM) and X-Ray are used to identify and determine the shape and size of the produced particles. Very stable sub-micrometric spherical particles for Au/PVP y Ag/PVP samples are obtained with diameters of 0.72 μ m y 0.40 μm, respectively. The preparation of colloids is performed in one step and no surfactant or dispersing agent is used in this process. <![CDATA[Density of modes maps for design of photonic crystal devices]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300193&lng=en&nrm=iso&tlng=en Abstract In the paper, we present numerical results on characterization of transmitting properties of wideband filters based on linear and nonlinear photonic crystals confined with the waveguide. Novel characteristics of the PhC filters such as density of modes maps and transmission maps are computed, and their efficiency is analyzed. Presented characteristics can be used as an auxiliary optimization tools to reduce optical losses when designing high-efficient optical interconnects. <![CDATA[Gravitational collapse in brane-worlds revisited]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300199&lng=en&nrm=iso&tlng=en Abstract This paper is dedicated to revisit the modifications caused by branes in the collapse of a stellar structure under the Snyder-Oppenheimer scheme. Due to the homogeneity and isotropy of the model, we choose study the case of a closed geometry described by k = 1, through the tool of dynamical systems. We revisit the different components of the star and its evolution during the stellar collapse, paying particular attention to the non-local effects and the quadratic terms of the energy momentum tensor that come from branes corrections. In the same vein we realize a phase portrait together with a stability analysis with the aim of obtain information about the attractors or saddle points of the dynamical system under different initial conditions in the density parameters, remarking the parameters that come from branes contributions. <![CDATA[Dissociation-ionization and ionization-dissociation by multiphoton absorption of acetaldehyde at 266 and 355 nm. Dissociation pathways]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300206&lng=en&nrm=iso&tlng=en Abstract The experimental results from the interaction of a sample of acetaldehyde (CH3CHO) with laser radiation at intensities between 109 and 1011Wcm2 and wavelengths of 266 and 355 nm are reported. As a result of multiple photon absorption, cations from ionization-dissociation (I-D) or dissociation-ionization (D-I) processes, were detected using a reflectron time of flight mass spectrometer. The processes I-D is predominant at 355 nm and D-I is predominant at 266 nm. The formation of different ions is discussed. From analysis of the ratios between the ion currents [I( C H 3 C O +)+I( C O +)]/[ I( C H 3 +)+I( H C O +)], originated from the C-C bond or from the C-H bond breaking at different laser intensities, the predominant channels are determined. <![CDATA[Cervical cancer detection based on serum sample surface enhanced Raman spectroscopy]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300213&lng=en&nrm=iso&tlng=en Abstract In the presence of nanoparticles, the Raman signal is enhanced to the levels sufficient to detect a single molecule, therefore spectroscopy Surface-Enhanced Raman Scattering (SERS) is currently recognized as a detection technique extremely sensitive with high levels of molecular specificity. This is the first report in the cervical cancer detection based on serum SERS. The serum samples were obtained from 14 patients who were clinically diagnosed with cancer and 14 healthy volunteer controls. The serum samples were mixed with colloidal silver nanoparticles of 40 nm in the same proportion, using sonication. About 10 spectra were collected of each serum sample using a Horiba Jobin-Yvon LabRAM Raman Spectrometer with a laser of 830 nm. The enhanced Raman bands allowed identifying biomolecules present at low concentration as amide I and III, carotene, glutathione, tryptophan, tyrosine and phenylalanine. Subsequently, the processed SERS spectra were analyzed using multivariate statistical analysis including principal component analysis and linear discriminant analysis (LDA). Preliminary results showed that SERS and PCA-LDA can be used to discriminate between cervical cancer and control samples with high sensitivity and specificity, forming an excellent support technique for current detection techniques.<hr/>Resumen En presencia de nanopartículas, la señal Raman se amplifica hasta niveles suficientes como para detectar una molécula individual, por tanto la espectroscopia Surface-Enhanced Raman Scattering (SERS) es actualmente reconocida como una técnica de detección extremadamente sensible con altos niveles de especificidad molecular. Este es el primer reporte en la detección del cáncer cervicouterino basado en la dispersión Raman de superficie amplificada de muestras de suero. Las muestras de suero fueron obtenidas de 14 pacientes quienes fueron clínicamente diagnosticadas con cáncer y 14 voluntarios saludables. Las muestras de suero y nanopartículas de plata de 40 nm en forma coloidal fueron mezcladas usando sonicación. Alrededor de 10 espectros SERS por cada paciente fueron recolectados usando un espectrómetro Raman LabRAM Horiba Jobin-Yvon con un láser de 830 nm. Las bandas Raman fuertemente amplificadas permitieron identificar biomoléculas presentes en bajas concentraciones como amidas I y III, carotenos, glutatión, triptófano, tirosina y fenilalanina. Posteriormente, los espectros SERS procesados fueron analizados utilizando análisis estadístico multivariado incluyendo análisis de componentes principales (PCA) y analisis de discriminante lineal (LDA). Resultados preliminares demostraron que SERS y PCA-LDA pueden ser usados para discriminar entre muestras control y cáncer cervicouterino con alta sensibilidad y especificidad, conformando una excelente técnica de apoyo para las actuales técnicas de detección. <![CDATA[GaN nanowires and nanotubes growth by chemical vapor deposition method at different NH<sub>3</sub> flow rate]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300219&lng=en&nrm=iso&tlng=en Abstract GaN nanowires and nanotubes have been successfully synthesized via the simple chemical vapor deposition method. NH3 flow rate was found to be a crucial factor in the synthesis of different type of GaN which affects the shape and the diameter of generated GaN nanostructures. X-ray diffraction confirms that GaN nanowires grown on Si(111) substrate under 900o C and with NH3 flow rate of 50 sccm presents the preferred orientation growth in the (002) direction. It is beneficial to the growth of nanostructure through catalyst annealing. Transmission electron microscopy and scanning electron microscopy were used to measure the size and structures of the samples. <![CDATA[Impact of planarized gate electrode in bottom-gate thin-film transistors]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300223&lng=en&nrm=iso&tlng=en Abstract In this work, the fabrication of bottom-gate TFTs with unplanarized and planarized gate electrode are reported, as well simulations of the impact of the gate planarization in the TFTs are presented. Previously in literature, a reduction of the contact resistance has been attributed to this planarized structure. In order to provide a physical explanation of this improvement, the electrical performance of ambipolar a-SiGe:H TFTs with planarized gate electrode by Spin-On Glass is compared with unplanarized ambipolar a-SiGe:H TFTs. Then, the properties in the main device interfaces are analyzed by physically-based simulations. The planarized TFTs have better characteristics such as field-effect mobility, on-current, threshold voltage and on/off-current ratio which are consequence of the improved contact resistance. <![CDATA[A nonextensive wavelet (<em>q,q´</em>)-entropy for 1/𝑓<sup>α</sup> signals]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300229&lng=en&nrm=iso&tlng=en Abstract This paper proposes a nonextensive wavelet ( q , q ' )-entropy computed as a wavelet-domain generalization of the time-domain ( q , q ' ) entropy of Borges and obtains a closed-form expression of this measure for the class of 1 / f α signals. Theoretical wavelet ( q , q ' )-entropy planes are obtained for these signals and the effect of parameters q and q ' on the shape and behaviour of these wavelet entropies are discussed with sufficient detail. The relationship of this entropy with Shannon and Tsallis entropies is studied and some applications of the proposed two-parameter wavelet entropy for the analysis/estimation of 1 / f signals are outlined. <![CDATA[Reduction of the Salpeter equation for massless constituents]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300235&lng=en&nrm=iso&tlng=en Abstract Different from the case of the limit, it is shown in this paper that in the ultrarelativistic limit, the L = j, j+1 wave components are large terms for both state with parity ȠP = (-1)j and state with parity ȠP = (-1)j+1. Moreover, it is found that the states with parity ȠP = (-1) j are degenerate with the states with parity ȠP = (-1) j +1 if the Lorentz structure of the interaction between the massless constituents is four-vector or time-component of four-vector. The scalar interaction violates this degeneracy. <![CDATA[Implications of the Ornstein-Uhlenbeck-like fractional differential equation in cosmology]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300240&lng=en&nrm=iso&tlng=en Abstract In this paper we introduce a generalized fractional scale factor and a time-dependent Hubble parameter obeying an “Ornstein-Uhlenbeck-like fractional differential equation” which serves to describe the accelerated expansion of a non-singular universe with and without the presence of scalar fields. Some hidden cosmological features were captured and discussed consequently. <![CDATA[Remarks on the (1+1)-Matrix-Branes, qubit theory and non-compact Hopf maps]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300251&lng=en&nrm=iso&tlng=en Abstract We discuss different aspects of a possible link between the (1+1)-matrix-brane system with qubit theory and non-compact Hopf maps. In these scenarios, the (2+2)-signature plays an important role. We argue that such links may shed some light on the (2+2)-dimensional sector of a (2+10)-dimensional target background. <![CDATA[Convergence of resonance expansions in quantum wave buildup]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300257&lng=en&nrm=iso&tlng=en Abstract The convergence of stationary and dynamical resonance expansions that involve complex eigenenergies of the system is analyzed in the calculation of the electronic probability density along the internal region of a resonant structure. We show that an appropriate selection of the resonance contributions leads to results that are numerically indistinguishable from the exact Hermitian calculation. In particular, the role played by the anti-resonances in the convergence process is emphasized. An interesting scaling property of the Schrödinger equation, and the stationary resonance expansion, useful for the analysis of convergence of families of systems, is also demonstrated. The convergence of a dynamical resonance expansion based on a Moshinsky shutter setup, is explored in the full time domain. In particular, we explore the build process of the electronic probability density in the transient regime, analyzing the contributions of different resonant states in the earliest stages of the buildup process. We also analyze the asymptotic limit of very long times, converging in the latter case to the stationary solution provided by the exact Hermitian calculation. <![CDATA[Additive and multiplicative noises acting simultaneously on Ermakov-Ray-Reid systems]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300267&lng=en&nrm=iso&tlng=en Abstract We investigate numerically the effect of additive and multiplicative noises on parametric oscillator systems of Ermakov-Ray-Reid type when both noises act simultaneously. We find that the main perturbation effects on the dynamical invariant of these systems are produced by the additive noise. Different from the separate action of the multiplicative noise when the dynamical invariant of these systems is robust, we also find a weak effect that can be attributed to the multiplicative noise.<hr/>Resumen Se investigan numéricamente los efectos de los ruidos aditivos y multiplicativos sobre los sistemas dinámicos de osciladores paramétricos de tipo Ermakov-Ray-Reid cuando los dos tipos de ruidos actúan de manera simultánea. La mayor parte de la perturbación del invariante proviene del ruido aditivo. A diferencia del caso cuando el ruido multiplicativo actúa por separado y el invariante dinámico presenta robustez, encontramos que en la acción simultánea de los dos ruidos hay también un efecto pequeño atribuible al ruido multiplicativo. <![CDATA[Performance of three violins made in Mexico evaluated through standard measurements from a legendary violin]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300271&lng=en&nrm=iso&tlng=en Abstract A set of Mexican violins handmade using traditional woods (i.e. spruce for the soundboard, maple for the body, and ebony for the fingerboard) were studied. Standard mobility measurements of these instruments were obtained, and the sound of each violin was recorded when a professional musician played a Bruch Concerto opening excerpt. One of the violins showed a mobility with high harmonic content remarking strong components of high frequencies, resembling the response of old Italian violins, and particularly one made by Stradivari; its sound was the brightest of the set. Meanwhile, other violin exhibited an opposite performance, with weak components of high frequency and having the darkest sound. The performance of the third violin was located between the other two, both in mobility and in its sound. The sound recordings are available for download; so these discussions can be actively judged by the reader. These Mexican violins covered a considerably different range of performance, so there is no reason to consider that violins made in Mexico could have some kind of limitation; quite the opposite, the results of this work show that obtaining a desired dynamical behavior (quantified by mobility measurements) of a new violin is totally feasible. <![CDATA[CO<sub>2</sub> measurement system based on pyroelectric detector]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300278&lng=en&nrm=iso&tlng=en Abstract CO2 concentration sensor based on the infrared (IR) absorption is presented, by using a pyroelectric detector the sample absorbed IR radiation is obtained and the CO2 concentration is calculated, system capabilities, sensibility, repeatibility and, time response of developed system are studied, results show that based on a photopyroelectric technique is possible to get an accurate CO2 measurement system. <![CDATA[Solution-processed transparent dielectric based on spin-on glass for electronic devices]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0035-001X2016000300282&lng=en&nrm=iso&tlng=en Abstract In this work, the fabrication and characterization of MOS and MIM capacitors using a solution-processed dielectric based on spin-on glass (SOG) solution is presented. The SOG solution is diluted with deionized water (DI) in order to make easier the evaporation of the organic material presented in the SOG. The films are highly transparent in the visible range, which makes feasible they use in transparent electronics. The capacitance-voltage and current-voltage characteristics of the MOS and MIM capacitors demonstrate the application of the solution-processed SOG/DI film as dielectric for electronic devices.