Site localization of Cd impurities in sapphire

By combining first-principles electronic structure calculations and existing time-differential gamma-gamma perturbed-angular-correlation experiments we studied the site localization, the local environment, and the electronic structure of Cd impurities in sapphire (alpha-Al2O3) single crystals in different charged states. The ab initio calculations were performed with the full-potential augmented plane wave plus local orbitals method and the projector augmented wave method. Comparing the calculated electric-field-gradient tensor at the Cd nuclei in the alpha-Al2O3 host lattice and the corresponding available experimental values, we have seen that it is equally possible for Cd to replace an Al atom (in a negative charge state) or to be placed in an interstitial site (in a neutral charge state). To finally address the issue of the Cd impurity localization, we performed formation energy calculations. These results have shown that Cd placed in the substitutional Al site, in the negatively charged state, is the most probable configuration.

DNA - novel nanomaterial for applications in photonics and in electronics

Functionalization with surfactants and with active molecules of deoxyribonucleic acid (DNA), thin film processing as well as their nonlinear optical and electrical properties are reviewed and discussed. On the basis of a quantum three level model, we show that the anomalous concentration variation of cubic susceptibility chi((3))(-3 omega; omega, omega, omega) in thin films of DNA-CTMA complexes doped with Disperse Red 1 chromophore can be explained by the concentration variation of two-photon resonance contribution. We show also that the DNA complexes, plasticized with glycerol and adequately doped can be processed into self standing conducting membranes with a high electrical conductivity. The measured ionic conductivity at room temperature, depending on dopant used and its concentration, is in the range of 3.5 x 10(-4)-10(-5) S/cm and increases linearly as a function of temperature, reaching 10(-3) S/cm at 358 K for the most conducting sample, obeying predominantly the Arrhenius law. Practical applications of DNA complexes are also described and discussed. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Development of Nanoinjector Devices for Electrospray Ionization - Tandem Mass Spectrometry (ESI-MSn)

In mass spectrometric (MS) systems with electrospray ionization (ESI), the sample can be analyzed coupled to separation systems (such as liquid chromatography or capillary electrophoresis) or simply by direct infusion. The greatest benefit of the type of injection is the possibility of continuous use of small amounts of samples over a long period of time. This extended analysis time allows a complete study of fragmentation by mass spectrometry, which is critical for structure elucidation of new compounds, or when using an ion trap mass analyzer. The injector filled with the sample is placed at the ESI source inlet creating an electric field suitable for the continuous formation of a spray (solvent and sample) and consequently, the gradual and even release of the sample. For the formation of the spray, is necessary that the injector end is metalized. The formation of a bilayer of titanium and gold provided an excellent attachment of the film, resulting in a nanoinjector for ionization/spray formation in the system for MS. The nanoinjectors showed high repeatability and stability over 100 min by continuous sampling with 10 mu L of sample.

Quantum motion in superposition of Aharonov-Bohm with some additional electromagnetic fields

The structure of additional electromagnetic fields to the Aharonov-Bohm field, for which the Schrodinger, Klein-Gordon, and Dirac equations can be solved exactly are described and the corresponding exact solutions are found. It is demonstrated that aside from the known cases (a constant and uniform magnetic field that is parallel to the Aharonov-Bohm solenoid, a static spherically symmetrical electric field, and the field of a magnetic monopole), there are broad classes of additional fields. Among these new additional fields we have physically interesting electric fields acting during a finite time or localized in a restricted region of space. There are additional time-dependent uniform and isotropic electric fields that allow exact solutions of the Schrodinger equation. In the relativistic case there are additional electric fields propagating along the Aharonov-Bohm solenoid with arbitrary electric pulse shape. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714352]

Turbulence driven particle transport in Texas Helimak

We analyze the turbulence driven particle transport in Texas Helimak [K. W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)], a toroidal plasma device with a one-dimensional equilibrium with magnetic curvature and shear. Alterations on the radial electric field, through an external voltage bias, change the spectral plasma characteristics inducing a dominant frequency for negative bias values and a broad band frequency spectrum for positive bias values. When applying a negative bias, the transport is high where the waves propagate with phase velocities near the plasma flow velocity, an indication that the transport is strongly affected by a wave particle resonant interaction. On the other hand, for positive bias values, the plasma has a reversed shear flow, and we observe that the transport is almost zero in the shearless radial region, an evidence of a transport barrier in this region. (c) 2012 American Institute of Physics. [doi:10.1063/1.3676607]

Formation and Characterization of Oriented Micro-and Nanofibers Containing Poly (ethylene oxide) and Pectin

Formation of oriented or aligned micro- and nanofibers using biocompatible materials opens the possibility to obtain engineered tissues that can be used in medicine, environmental engineering, security and defense, among other applications. Pectin, a heteropolysaccharide, is a promising material to be incorporated into the fibers because, besides being biocompatible, this material is also biodegradable and bioactive. In this work, the formation of oriented fibers using solutions containing pectin and polyethylene oxide (biocompatible polymers), and chloroform (as the solvent) is investigated. The injection of solution into an intense electric field defined between two parallel electrodes was used to obtain oriented fibers. This novel approach is a modification of the conventional electrospinning process. The presence of pectin in the fibers was confirmed by FTIR analysis. Fibers with diameters of hundreds of nanometers and several centimeters long can be collected. The incorporation of pectin leads to a higher variation of the diameter of the fibers, and a trend to larger fiber diameters. This behavior can be related to the presence of pectin clusters in the fibers. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.057203jes] All rights reserved.

On the optical properties of copper nanocubes as a function of the edge length as modeled by the discrete dipole approximation

This Letter reports an investigation on the optical properties of copper nanocubes as a function of size as modeled by the discrete dipole approximation. In the far-field, our results showed that the extinction resonances shifted from 595 to 670 nm as the size increased from 20 to 100 nm. Also, the highest optical efficiencies for absorption and scattering were obtained for nanocubes that were 60 and 100 nm in size, respectively. In the near-field, the electric-field amplitudes were investigated considering 514, 633 and 785 nm as the excitation wavelengths. The E-fields increased with size, being the highest at 633 nm. (c) 2012 Elsevier B.V. All rights reserved.

Disposable polyester-toner electrophoresis microchips for DNA analysis

Microchip electrophoresis has become a powerful tool for DNA separation, offering all of the advantages typically associated with miniaturized techniques: high speed, high resolution, ease of automation, and great versatility for both routine and research applications. Various substrate materials have been used to produce microchips for DNA separations, including conventional (glass, silicon, and quartz) and alternative (polymers) platforms. In this study, we perform DNA separation in a simple and low-cost polyester-toner (PeT)-based electrophoresis microchip. PeT devices were fabricated by a direct-printing process using a 600 dpi-resolution laser printer. DNA separations were performed on PeT chip with channels filled with polymer solutions (0.5% m/v hydroxyethylcellulose or hydroxypropylcellulose) at electric fields ranging from 100 to 300Vcm(-1). Separation of DNA fragments between 100 and 1000 bp, with good correlation of the size of DNA fragments and mobility, was achieved in this system. Although the mobility increased with increasing electric field, separations showed the same profile regardless of the electric field. The system provided good separation efficiency (215 000 plates per m for the 500 bp fragment) and the separation was completed in 4 min for 1000 bp fragment ladder. The cost of a given chip is approximately $0.15 and it takes less than 10 minutes to prepare a single device.

Self-potential signals from an analog biogeobattery mode

A tank experiment was conducted to check if self-potential (SP) signals can be generated when buried organic matter is wire-connected to a near-surface, oxygen-rich, sediment layer. This experiment demonstrated that once wired, there was a flux of electrons (hence an electric current) between the lower and upper layers of the sandbox with the system responding as a large-scale microbial fuel cell (a type of bioelectrochemical system). An electric current was generated by this process in the wire and the SP method was used to monitor the associated electric potential distribution at the top of the tank.. The electric field was controlled by the flux of electrons through the wire, the oxidation of the organic matter, the reduction of oxygen used as a terminal electron acceptor, and the distribution of the DC resistivity in the tank. The current density through the wire was limited by the availability of oxygen and not by the oxidation of the organic matter. This laboratory experiment incorporated key elements of the biogeobattery observed in some organic-rich contaminant plumes. This analogy includes the generation of SP signals associated with a flux of electrons, the capacity of buried organic matter in sustaining anodic reactions, network resistance connecting terminal redox reactions spatially separated in space, and the existence of anodic secondary coupled reactions. A resistivity tomogram of the tank, after almost a year in operation, suggests that oxidative processes triggered by this geobattery can be imaged with this method to determine the radius of influence of the bioelectrochemical system.

Development of nanoinjector devices for electrospray ionization - tandem mass spectrometry (ESI-MSn)

In mass spectrometric (MS) systems with electrospray ionization (ESI), the sample can be analyzed coupled to separation systems (such as liquid chromatography or capillary electrophoresis) or simply by direct infusion. The greatest benefit of the type of injection is the possibility of continuous use of small amounts of samples over a long period of time. This extended analysis time allows a complete study of fragmentation by mass spectrometry, which is critical for structure elucidation of new compounds, or when using an ion trap mass analyzer. The injector filled with the sample is placed at the ESI source inlet creating an electric field suitable for the continuous formation of a spray (solvent and sample) and consequently, the gradual and even release of the sample. For the formation of the spray, is necessary that the injector end is metalized. The formation of a bilayer of titanium and gold provided an excellent attachment of the film, resulting in a nanoinjector for ionization/spray formation in the system for MS. The nanoinjectors showed high repeatability and stability over 100 min by continuous sampling with 10 µL of sample.

Analysis of Electrostatic Turbulence Drive in Texas Helimak.

Plasma turbulence and particle transport in Texas Helimak change with the radial electric field profile modified by an external voltage bias. When the bias is positive, the turbulence shows enhanced level and broadband spectra with extreme events, similar to the turbulence in tokamak scrape-‐off layer. However, negative bias reduces the turbulence level and decreases the spectrum widths. Moreover, for negative biased shots, the particle transport is strongly affected by a wave particle resonant interaction. On the other hand, for positive bias values, the plasma presents a transport barrier in the reversed shear flow region.

Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties

Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process. The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.

Estudio de estructuras microtira irregulares mediante el MoM

[EN]This article presents the analysis of planar mi- crostrip structures using the electric-field integral equation. The structures are divided into irregular rectangular subdomains. Besides its describes the delta-gap voltage excitation mode to resolve the equations systems with the method of the moments.

Diagnostic techniques for EHD and MHD interaction

The impact of plasma technologies is growing both in the academic and in the industrial fields. Nowadays, a great interest is focused in plasma applications in aeronautics and astronautics domains. Plasma actuators based on the Magneto-Hydro-Dynamic (MHD) and Electro- Hydro-Dynamic (EHD) interactions are potentially able to suitably modify the fluid-dynamics characteristics around a flying body without utilizing moving parts. This could lead to the control of an aircraft with negligible response time, more reliability and improvements of the performance. In order to study the aforementioned interactions, a series of experiments and a wide number of diagnostic techniques have been utilized. The EHD interaction, realized by means of a Dielectric Barrier Discharge (DBD) actuator, and its impact on the boundary layer have been evaluated by means of two different experiments. In the first one a three phase multi-electrode flat panel actuator is used. Different external flow velocities (from 1 to 20m/s) and different values of the supplied voltage and frequency have been considered. Moreover a change of the phase sequence has been done to verify the influence of the electric field existing between successive phases. Measurements of the induced speed had shown the effect of the supply voltage and the frequency, and the phase order in the momentum transfer phenomenon. Gains in velocity, inside the boundary layer, of about 5m/s have been obtained. Spectroscopic measurements allowed to determine the rotational and the vibrational temperature of the plasma which lie in the range of 320 ÷ 440°K and of 3000 ÷ 3900°K respectively. A deviation from thermodynamic equilibrium had been found. The second EHD experiment is realized on a single electrode pair DBD actuator driven by nano-pulses superimposed to a DC or an AC bias. This new supply system separates the plasma formation mechanism from the acceleration action on the fluid, leading to an higher degree of the control of the process. Both the voltage and the frequency of the nano-pulses and the amplitude and the waveform of the bias have been varied during the experiment. Plasma jets and vortex behavior had been observed by means of fast Schlieren imaging. This allowed a deeper understanding of the EHD interaction process. A velocity increase in the boundary layer of about 2m/s had been measured. Thrust measurements have been performed by means of a scales and compared with experimental data reported in the literature. For similar voltage amplitudes thrust larger than those of the literature, had been observed. Surface charge measurements led to realize a modified DBD actuator able to obtain similar performances when compared with that of other experiments. However in this case a DC bias replacing the AC bias had been used. MHD interaction experiments had been carried out in a hypersonic wind tunnel in argon with a flow of Mach 6. Before the MHD experiments a thermal, fluid-dynamic and plasma characterization of the hypersonic argon plasma flow have been done. The electron temperature and the electron number density had been determined by means of emission spectroscopy and microwave absorption measurements. A deviation from thermodynamic equilibrium had been observed. The electron number density showed to be frozen at the stagnation region condition in the expansion through the nozzle. MHD experiments have been performed using two axial symmetric test bodies. Similar magnetic configurations were used. Permanent magnets inserted into the test body allowed to generate inside the plasma azimuthal currents around the conical shape of the body. These Faraday currents are responsible of the MHD body force which acts against the flow. The MHD interaction process has been observed by means of fast imaging, pressure and electrical measurements. Images showed bright rings due to the Faraday currents heating and exciting the plasma particles. Pressure measurements showed increases of the pressure in the regions where the MHD interaction is large. The pressure is 10 to 15% larger than when the MHD interaction process is silent. Finally by means of electrostatic probes mounted flush on the test body lateral surface Hall fields of about 500V/m had been measured. These results have been used for the validation of a numerical MHD code.

Vortex dynamics in the high-temperature superconductors YBa 2 Cu 3 O 7 and Bi 2 Sr 2 CaCu 2 O 8 + delta in low- and high-dissipative transport measurements

This thesis investigates phenomena of vortex dynamics in type II superconductors depending on the dimensionality of the flux-line system and the strength of the driving force. In the low dissipative regime of Bi_2Sr_2CaCu_2O_{8+delta} (BSCCO) the influence of oxygen stoichiometry on flux-line tension was examined. An entanglement crossover of the vortex system at low magnetic fields was identified and a comprehensive B-T phase diagram of solid and fluid phases derived.In YBa_2Cu_3O_7 (YBCO) extremely long (>100 mm) high-quality measurement bridges allowed to extend the electric-field window in transport measurements by up to three orders of magnitude. Complementing analyses of the data conclusively produced dynamic exponents of the glass transition z~9 considerably higher than theoretically predicted and previously reported. In high-dissipative measurements a voltage instability appearing in the current-voltage characteristics of type II superconductors was observed for the first time in BSCCO and shown to result from a Larkin-Ovchinnikov flux-flow vortex instability under the influence of quasi-particle heating. However, in an analogous investigation of YBCO the instability was found to appear only in the temperature and magnetic-field regime of the vortex-glass state. Rapid-pulse measurements fully confirmed this correlation of vortex glass and instability in YBCO and revealed a constant rise time (~µs).