A novel red phosphor Ba2ZnSi2O7:Eu3+ has been synthesized by sol-gel method. The crystallinity, particle size, morphology, chemical composition and luminescent properties were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), energy-dispersion spectrum (EDS) and spectrofluorometer, respectively. The results of thermogravimetric (TG) and XRD indicated that the Ba2ZnSi2O7:Eu3+ phosphors crystallized completely at 900 °C. The luminescent properties of phosphor showed red emission is obtained by exciting at 394 and 465 nm which are owing to the sharp 7F0$\to$5L6 and 7F0$\to$5D2 lines of Eu3+. Two strongest lines at 394 and 465 nm in excitation spectra of the phosphor match well with the two popular emissions from near-ultraviolet (UV) and blue GaN-based light emitting diodes (LEDs), so it could be used as red components for white LEDs.

The cathodoluminescence spectrum of n-GaN crystal has been studied with emphasis placed on its self-absorption behavior. An improved analysis of cathodoluminescence spectral shift with electron penetration depth is shown, according to the following approach: (i) a main band and a sub-band, both of Gaussian nature, are used for spectral convolution; (ii) the observed absorption edge is still described in terms of the Urbach rule, but the Urbach tail is experimentally retrieved by directly using the absorption spectrum (at low energies) obtained from standard cathodoluminescence spectra; (iii) an experimental approach is used to retrieve the actual morphology of the cathodoluminescence probe.

In this article we present an alternative explanation of the phenomenon of wire fragmentation under high transient currents based on classical electromagnetism. We also explain how this phenomenon can be utilized as a primitive example of low energy-high power disruptive phenomena that can affect even nuclear matter.

The effect of structural disorder under bias voltage on the transmission properties of a non-interacting electron across multibarrier systems (GaAs/AlxGa$_{1-x}$As) is exhaustively studied by a computational model using exact Airy function formalism and the transfer-matrix technique. In ordered systems we study the effect of bias voltage on miniband structure. For disordered structures we investigate the transmission coefficient. Different types of eigenstates are obtained, those having a very low Lyapunov exponent close to the resonant energy and those with high slope in other region. Commuting resonance energy is theoretically demonstrated in this paper, the obtained values are in good agreement with the existing numerical results.

Multiwalled carbon nanotubes are grown on nickel-seeded silicon substrates using plasma-enhanced chemical vapor deposition method at a temperature of 650 °C utilizing a mixture of acetylene and hydrogen. Magnetic and electric fields were used to obtain well-oriented carbon nanotubes. The direction of growth was found to strongly depend on the directions and magnitudes of the applied fields. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) have been used to investigate the grown nanotubes. The SEM and TEM images of as grown nanotubes show that applying magnetic field during the growth process affects the growth direction of the nanotubes and, furthermore, bent nanotubes can be achieved by changing the direction of the applied electric field alone. Raman spectroscopy has been used to analyze the structure of the samples.  

Analysis of applied magnetic field and electrical current in Magnetohydrodynamic (MHD) accelerator due to electrical efficiency has been numerically investigated. Studies were carried out using air plasma as a working gas in equilibrium condition. Composition of simulated air-plasma consists of two species, N2, and O2, with concentration of 1 mol and 0.284 mol, respectively. The working gas is seeded with potassium and seed fraction is 1% by weight of all gas, which corresponds to 0.949% in mole ratio. In order to solve the set of differential equations with MHD approximations, the MacCormack scheme is employed. The Magnetohydrodynamic Augmented Propulsion Experiment (MAPX) channel designed and developed by NASA MSFC is used to investigate the MHD accelerator performance. Numerical results show the characteristic of MHD accelerator electrical efficiency with variation of different applied magnetic field and electrical input.

We report a novel technique to broaden and reshape the spectrum of picosecond laser pulse based on the seeder of gain switch laser diode and Yb3+-doped fiber amplifier (YDFA). From compensating the seed spectrum with the gain of YDFA, the seed pulse of 7 nm bandwidth is broadened to 20 nm, and the flat top spectral shape is obtained as well. A self-made fiber coupled tunable filter is used to realize the tunable output laser with the wavelength range from 1053 nm to 1073 nm and the line width of 1.4 nm.

We propose a new technique for measuring the frequency stability of cw laser radiation. The technique relies on using the laser to be tested as a coupling laser in a scheme of electromagnetically-induced transparency (EIT), either on a $\Lambda $ or a ladder system. A second, frequency tunable laser (stabilization of this laser is not needed) is used both to act as the EIT probe laser, and to form an atomic frequency reference spectrum. The frequency stability is monitored via the frequency deviation of the EIT resonance with respect to an atomic reference frequency. We also present an improved dichroic atomic vapor laser lock (DAVLL) method for frequency stabilization based on a nanocell with a $\lambda /2$ thickness.

A device for measuring total electron yields in the energy range 4–65 keV from conductor was set up successfully, which was made up of electron gun system, vacuum system and electrical system. By the pulse electron gun method, the total electron yields in the energy range 4–65 keV from silver were measured, based on the relation between the secondary electron yield and total electron yield at high incident electron energy from metals, the secondary electron yields in the energy range 10–65 keV from silver were deduced. Total electron yields measured with the device were compared with theoretical values, and the deduced secondary electron yield were compared with several authors' values, the results were discussed and a conclusion was drawn that the deduced secondary electron yields and the total electron yields from silver measured with the device are credible.

This study reports our numerical simulation of light extraction efficiency enhancement for a single quantum well by Extraordinary Optical Transmission (EOT) induced by a silver plate with air slit array. Our numerical experiment indicates that the enhancing effect could depend on a series of factors, namely, the nature of EOT, the polarizations and the positions of the quantum wells. Only by using TM polarized source significant enhancement can be achieved, and the enhancement excited by Fabry-Perot resonance is greater than that by surface plasmon polaritons; yet moving the source off the Ag/GaN interface will have the enhancement weakened. Position of the source, to be specific, either below an air slit or a silver strip, can lead to quite different results; and the greatest enhancement occurs when the source is placed right below the air slit.

The defect structure and the EPR parameters (the g factors, the hyperfine structure constants and the superhyperfine parameters) for the tetragonal Ir2+ center in AgBr are theoretically investigated using the perturbation formulas of these parameters for a 5d7 ion in tetragonally elongated octahedra. In the calculations, the contributions from the ligand orbital and spin-orbit coupling interactions and the local lattice (elongation) distortion due to the Jahn-Teller effect are taken into account. Related molecular orbital coefficients and the ligand unpaired spin densities are determined quantitatively using a cluster approach. The impurity center is attributed to the substitutional [ IrBr6] 4− cluster on host Ag+ site, which suffers the relative elongation of about 0.08 Å along C4 axis due to the Jahn-Teller effect. The calculated EPR parameters based on the above Jahn-Teller elongation show good agreement with the observed values.

Angle-resolved reflection spectroscopy is used to study surface plasmon polariton modes of metallic gratings consisting of sub-wavelength grooves. The used optical set-up allows recording of zero and m = −1 order reflection spectra in the visible and near infra-red spectral region. The different modes and their mutual coupling was identified in the dispersion diagram by means of modal theory. Surface plasmon modes at the grating surface and cavity modes in the sub-wavelength grooves were evidenced.

The eddy current testing method is widely used to evaluate conductive pieces. This method requires an adequate mathematical model which is able to describe the complicated interactions between the source and induced currents, primary and secondary, the fields and the flaws in materials. This paper describes a model which predicts the apparent changes in the impedance of an absolute ferrite-cored probe in axially symmetric non destructive testing (NDT) configurations. Originally, this model is based on coupled electromagnetic quantities principle. To include the contribution of the magnetic environment, the state variable chosen is the current because the magnetic magnetization is replaced by the fictional equivalent currents. The obtained modelling results are validated by comparison to finite element computations. Once validated, the suggested model is not only applied to calculation of probe's impedance in the presence of a defect inside the load but it is also applied to determine geometrical and physical characteristics of the eddy current non destructive testing (ECNDT) device. This half-numerical technique with a very weak time of simulation can be used for the design of new probes and offers a simple solution to the inversion problem. The model is implemented within a software tool (CECM: coupling electromagnetic circuits method) developed in MATLAB environment.

The influence of cooling rate on the structure, melting, hardness and indentation creep behavior of the Sn-0.7Cu-0.5Zn lead-free solder alloy has been studied by XRD, DSC and Vickers microhardness tester, respectively. The study was carried out for the alloy prepared at two different cooling rates of 3.5 °C/s and 11.7 × 10−3 °C/s. The results showed that the cooling rate significantly affects the structure, melting and mechanical properties of this alloy. Cu atoms are restricted in the formation of the intermetallic compound (IMC) Cu6Sn5 embedded in Sn-matrix in the slow cooled sample. Cu3Sn compound was detected in the fast cooled sample. The Zn-phase has not been detected by the X-ray diffraction analysis, which means a complete solubility of Zn in Sn-matrix has been obtained. The crystallite size of the Sn-matrix phase in the slow cooled sample was found to be 54.4 nm, while the value of the fast cooled sample was found to be 48.5 nm. This means the fast cooling condition caused grain refinement. This refinement leads to decrease the melting point from 222.7 to 221.2 °C and increase microhardness from 16.4 to 18.2 kg/mm2. Furthermore, fast cooling condition improved the creep resistance of Sn-0.7Cu-0.5Zn alloy than that of the slow cooling condition.

An analytical iterative algorithm for fast computation of scattering from multiple conductive cylinders is developed. It takes account of the independent 1st-order, coupling 2nd-order and higher-order scattering of multiple objects. The 1st-order scattering, as independent scattering of a single object self, is derived by using the expansion of cylindrical waves in local coordinate of the object, which are solved by the boundary conditions. Exciting by the 1st-order scattering from one object, the 2nd-order scattering of multi-objects are obtained iteratively using the addition theorem of Hankel function and the boundary conditions. The same approach is applicable to calculations of the 3rd-order and higher order scattering. It is found that the phase differences caused by the cylinder centers indicate the scattering wave interferences of multi-objects. Comparison with numerical MoM results well validates the analytical iterative algorithm, which significantly accelerates the scattering computation for wide-band frequencies f and overall azimuth angles θ over 360°. In order to depress the ringing effect caused by the abrupt change of scattering field in computed region to zero field in uncomputed region, the Hamming window is used to make gradual change of the scattering field to zero. Using FFT and 2D spline interpolation, discrete scattering data over the $f-\theta$ plane yield uniform discrete data over the X − Y plane. The image reconstruction is finally performed for multiple conductive cylinders. The image can well identify the positions and sizes of multi-objects.

Mechanical abrasion is a phenomenon which commonly occurs during the application of polar-molecular electrorheological (PMER) fluids. We experimentally investigate its effect by milling PMER particles for different times. We find that this effect can significantly reduce electrorheological effects of PMER fluids made of butyrolactone-modified TiO2 particles. This reduction results from the reduced interaction between PMER particles due to the loss of polar molecules on the surface of TiO2 particles. It is further revealed that adding proper amount of suitable polar molecules to the host fluid may compensate for the reduction of yield stress which can be about 100% at high electric fields.

Two simulation methods of the energy transmitted by the arc roots to the electrode material are described and their results are compared together and with these found by other authors. About a copper electrode the time phase evolutions are given when a constant energy flux is applied to the contact surface. The obtained results are better for vacuum and small current. The cathode and anode result discussions lead to propositions to improve arc root models.

Depleted uranium (U$^{238})$ is used for pre-ionization in the neon gas to study the soft X-ray emission in a Mather type plasma focus of 3.3 kJ. The X-rays are detected using an assembly of Quantrad Si pin diodes, masked with differential Ross fitters, and with a multi pinhole camera. The X-ray yield and pinhole images are found strongly influenced by the preionization and the pressure of the working gas. The soft X-ray yield of 82.5 ± 4.0 J in 1.3–1.56 keV energy window is obtained in the case of preionization of neon gas at the optimum pressure of 5 mbar, leading to the conversion efficiency of 2.5% of the stored energy. The total yield with preionization is 195 ± 9.0 J in 4π geometry measured at the optimum pressure of 5 mbar giving conversion efficiency of 5.9%. The time integrated images indicate the broadening of X-ray emission zone with preionization.

Piezoelectric elements can be used to harvest electrical energy when impact forces are applied to their surfaces. Often, however, only the peak voltages, or peak power output is used as a measure of device performance, and the total energy harvested during an impact force is overlooked. For energy harvesting applications, such as small-scale piezoelectric batteries, the total energy generated over an impact cycle should be considered. In this paper the total energy efficiency of several commercially available piezoelectric materials are evaluated using impact testing. The results revealed that different materials have significantly different energy efficiencies due to factors such as material type and device construction. Further, it was found that peak power output is not always the most appropriate measure of device performance for energy conversion applications.

In this article the dynamic mechanical characterization of PDMS and SU8 resin using dynamic mechanical analysis, nanoindentation and the scanning microdeformation microscope have been presented. The methods are hereby explained, extended for viscoelastic behaviours, and their compatibility underlined. The storage and loss moduli of these polymers over a wide range of frequencies (from 0.01 Hz to some kHz) have been measured. These techniques are shown fairly matching and the two different viscoelastic behaviours of these two polymers have been exhibited. Indeed, PDMS shows moduli which still increase at 5 kHz whereas SU8 ones decrease much sooner. From a material point of view, the Havriliak and Negami model to estimate instantaneous, relaxed moduli and time constant of these materials has been identified.