Study of random telegraph signals in a GaAs/AlxGa1 − xAs single electron transistor

A GaAs/Al_xGa_1 − xAs heterointerface contains charge traps, which can capture and emit a single electron stochastically. We study random telegraph signals (RTSs) from these traps using a single electron tunneling (SET) transistor formed in the heterostructure. The output of the SET transistor switches between two states, corresponding to the capture and emission of a single electron. The occurrence of RTS depends on the variation in the potential modified by negatively biased Schottky gates. These gate voltage dependences indicate the spatial positions of traps. Moreover, we investigate the interaction between trappings.     

Electret properties of ethylene–propylene random co-polymer

Thermally stimulated current (TSC) spectra were examined for ethylene–propylene (EP) random co-polymer at different charging voltages V_p with positive and negative polarities. Observed TSC spectra showed two well-separated TSC bands, B_L and B_H, which respectively appeared in the temperature regions below and above 100 °C. Observed V_p dependence of B_L was quite different from that of typical polypropylene homo-polymer: As V_p increased, B_L band grew keeping its peak position same at 65 °C, and the band shape unchanged, as if the traps responsible for the B_L band are a single set of traps with the same trap depth and capture cross section. The trap depth of B_L was about 1.9 eV and 1.7 eV for positively charged EP and talc-containing EP samples, respectively. EP samples also showed unique TSC bands above 100 °C: one is a narrow TSC band peaked at 120 °C and the other is an unusual TSC band which was non-vanishing even at 165 °C just before destruction of samples by their melting. Consequently, the utmost stable charge density in EP co-polymer above 100 °C was found to be 3.5 × 10^?4 C/m² and 6.0 × 10 ^?4 C/m² for positively and negatively charged samples, respectively. These equivalent surface charge densities are much larger than those of usual polypropylene homo-polymer.     

Geometry dependent resistivity behavior in mesoscopic Bi2Sr2CaCu2O8+δ single crystals

In order to investigate the interaction between Josephson vortices and pancake vortices in a layered Bi₂Sr₂CaCu₂O_8+δ superconductor, c-axis resistivity measurements were carried out on fabricated mesoscopic single crystals for two experimental geometries, when an applied high magnetic field of 14 T is perpendicular (B_ex⊥L) and parallel (B_ex∥L) to the width of sample. In the first case, the angular dependence of the resistance obtained near the ab-plane at T = 30 K exhibited hysteretic non-monotonic behavior with local maxima at θ = 0.6° away from the ab-plane and dips and spikes at θ = 0.2° marking a vortex lock-in transition. In the second geometry (B_ex∥L), instead of a local maximum, peculiar resistance shoulders were observed. At higher temperatures, hysteresis is reduced, while the vortex lock-in transition becomes considerably broader indicating the interaction of pancake and Josephson vortices.     

Interaction of dioxouranium(VI) ion with EDTA at different ionic strengths

The formation of complex species of dioxouranium(VI) ion with EDTA was studied in the pH range of 1–3.5 and at 25 °C using a combination of potentiometric and spectrophotometric techniques. Results showed evidence for formation of the following species: [UO₂H₄EDTA]²⁺, [UO₂H₃EDTA]⁺, and [UO₂H₂EDTA]. Investigations were performed in sodium perchlorate as background electrolyte at 0.1, 0.3, 0.5, 0.7, and 1.0 mol dm^? 3. The parameters based on the formation constants were calculated, and the dependences of protonation and the stability constants on ionic strength are described. The dependence on ionic strength of the formation constants was analyzed using the specific ion interaction theory (SIT) model. The stability constant values at infinite dilution, obtained using SIT model, are log β°₁₄₁ = 6.77, log β°₁₃₁ = 5.99 and log β°₁₂₁ = 9.29, where indexes for the overall stability constant, β_pqr, refer to the equilibrium pUO₂²⁺ + qH⁺ + rL^4? ? M_pH_qL_r^{(2p + q ? 4r)}. The specific interaction coefficients are also reported.     

CUDA accelerated method for motion correction in MR PROPELLER imaging

In PROPELLER, raw data are collected in N strips, each locating at the center of k-space and consisting of M_x sampling points in frequency encoding direction and L lines in phase encoding direction. Phase correction, rotation correction, and translation correction are used to remove artifacts caused by physiological motion and physical movement, but their time complexities reach O(M_x × M_x × L × N), O(N × R_A × M_x × L × (M_x × L + R_N × R_N)), and O(N × (R_N × R_N + M_x × L)) where R_N × R_N is the coordinate space each strip gridded onto and R_A denotes the rotation range. A CUDA accelerated method is proposed in this paper to improve their performances. Although our method is implemented on a general PC with Geforce 8800GT and Intel Core(TM)2 E6550 2.33 GHz, it can directly run on more modern GPUs and achieve a greater speedup ratio without being changed. Experiments demonstrate that (1) our CUDA accelerated phase correction achieves exactly the same result with the non-accelerated implementation, (2) the results of our CUDA accelerated rotation correction and translation correction have only slight differences with those of their non-accelerated implementation, (3) images reconstructed from the motion correction results of CUDA accelerated methods proposed in this paper satisfy the clinical requirements, and (4) the speed up ratio is close to 6.5.     

Microfabrication of solenoid-type RF SMD chip inductors with an Al2O3 core

We investigated micron size, high-performance, and solenoid-type radio-frequency surface-mounted device (SMD) chip inductors with a low-loss Al₂O₃ core for a GHz drive microwave circuit application. Copper coils with a diameter of 27 μm were used and the chip inductors fabricated in this study are 0.86 × 0.46 × 0.45 mm³. The high-frequency characteristics of the inductance (L), quality factor (Q), and impedance (Z) of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with HP16193A test fixture). The developed inductors have a self-resonant frequency of 3.7–5.2 GHz and exhibit L of 15–34 nH. The inductors have Q of 38–49 over the frequency ranges of 900 MHz–1.7 GHz. The calculated data obtained from the equivalent circuit and the derived equation of Q described the high-frequency data of L, Q, and Z of the inductors developed quite well.     

Ultrasonic assisted-Fenton-like degradation of nitrobenzene at neutral pH using nanosized oxides of Fe and Cu

Ultrasonic-assisted heterogeneous Fenton reaction was used for degradation of nitrobenzene (NB) at neutral pH conditions. Nano-sized oxides of α-Fe₂O₃ and CuO were prepared, characterized and tested in degradation of NB (10 mg L⁻¹) under sonication of 20 kHz at 25 °C. Complete degradation of NB was effected at pH 7 in presence of 10 mM H₂O₂ after 10 min of sonication in presence of α-Fe₂O₃ (1.0 g L⁻¹), (k = 0.58 min⁻¹) and after 25 min in case of CuO (k = 0.126 min⁻¹). α-Fe₂O₃ showed also effective degradation under the conditions of 0.1 g L⁻¹ oxide and 5.0 mM of H₂O₂, even though with a lower rate constant (0.346 min⁻¹). Sonication plays a major role in enhancing the production of hydroxyl radicals in presence of solid oxides. Hydroxyl radicals-degradation pathway is suggested and adopted to explain the differences noted in rate constants recorded on using different oxides.     

Electromagnetically Induced Transparency and optical pumping processes formed in Cs sub-micron thin cell

The Electromagnetically Induced Transparency (EIT) effect in a Λ-system formed by Cs atoms (6S_1/2 ? 6P_3/2 ? 6S_1/2) confined in an extremely thin cell (ETC) (atomic column thickness L varies in the range of 800 nm –3 µm is studied both experimentally and theoretically. It is demonstrated that when the coupling laser frequency is in exact resonance with the corresponding atomic transition, the EIT resonance parameters weakly depend on L, which allows us to detect the effect at L = λ = 852 nm. EIT process reveals a striking peculiarity in case of the coupling laser detuned by Δ from the atomic transition, namely the width of the EIT resonance rapidly increases upon an increase in Δ (an opposite effect is observed in centimeter-scale cells). The strong broadening of the EIT resonance for large values of detunings Δ is caused by the influence of atom-wall collisions on dephasing rate of coherence. The influence of the coupling laser on the velocity selective optical pumping/saturation resonances formed in ETC has been also studied. The theoretical model well describes the observed results.     

Optimization considerations for a SASE free electron laser based on a superconducting undulator

A self amplified spontaneous emission (SASE) free electron laser (FEL) based on a new generation superconducting planar undulator, is optimized. It is shown that the laser wavelength should be down to soft X-rays range (～2–3 nm) of the spectrum via a dedicated undulator driven by a 1 GeV electron linear accelerator (linac). Numerical calculations and simulation results of the three main performance parameters for SASE operation, namely 1D gain length (L_G,1D), saturation power (P_sat) and saturation length (L_sat), are compared and discussed.     

Raman scattering from confined phonons in GaAs/AlGaAs quantum wires

We report on photoluminescence and Raman scattering performed at low temperature (T =  10 K) on GaAs/Al_0.3Ga_0.7As quantum-well wires with effective wire widths ofL =  100.0 and 10.9 nm prepared by molecular beam epitaxial growth followed by holographic patterning, reactive ion etching, and anodic thinning. We find evidence for the existence of longitudinal optical phonon modes confined to the GaAs quantum wire. The observed frequency at ο_L10 =  285.6 cm⁻¹forL =  11.0 nm is in good agreement with that calculated on the basis of the dispersive dielectric continuum theory of Enderleinas applied to the GaAs/Al_0.3Ga_0.7As system. Our results indicate the high crystalline quality of the quantum-well wires fabricated using these techniques.     

Preparation of enzyme nanoparticles and studying the catalytic activity of the immobilized nanoparticles on polyethylene films

Using high-intensity ultrasound, in situ generated α-amylase nanoparticles (NPs) were immobilized on polyethylene (PE) films. The α-amylase NP-coated PE films have been characterized by E-SEM, FTIR, DLS, XPS and RBS. The PE was reacted with HNO₃ and NPs of the α-amylase were also deposited on the activated PE. The PE impregnated with α-amylase (4 μg per 1 mg PE) was used for hydrolyzing soluble potato starch to maltose. The immobilization improved the catalytic activity of α-amylase at all the reaction conditions studied. The kinetic parameters, K_m (5 and 4 g L^?1 for the regular and activated PE, respectively) and V_max (5 × 10^?7 mol ml^?1 min^?1, almost the same numbers were obtained for the regular and activated PEs) for the immobilized amylase were found to slightly favor the respective values obtained for the free enzyme (K_m = 6.6 g L^?1, V_max = 3.7 × 10^?7 mol ml^?1 min^?1). The enzyme remained bound to PE even after soaking the PE in a starch solution for 72 h and was still found to be weakly active.     

Hump structure below Tc in the thermal conductivity of MgB2 superconductor

A reasonable cause of absence of hump structure in thermal conductivity of MgB₂ below the superconducting transition temperature (T_c) lies in the appearance of multigap structure. The gaps of lower magnitude can be suppressed by defects so that this system becomes effectively a single-gap superconductor. When such a situation is created, it is hoped that thermal conductivity (κ) will show hump below T_c. Proceeding along these lines, a sample of MgB₂ with a relatively higher residual resistivity ρ_o = 33.8 μΩ cm has been found to show a hump structure below T_c. The actual electronic thermal conductivity κ_el of this sample is less than that expected from the Wiedeman–Franz law by more than a factor of 2.6 in the considered temperature range.Modifying the Wiedeman–Franz law for the electronic contribution by replacing the Lorenz number L₀ = 2.45 × 10^?8 W Ω K^?2 by an effective Lorenz number L_eff (<L₀) we have obtained two sets of κ_el, namely those with L_eff = 0.1L₀ and 0.2L₀. Corresponding to these two sets of κ_el, two sets of the phonon thermal conductivity κ_ph are obtained. κ_ph has been analyzed in terms of an extended Bardeen–Rickayzen–Tewordt theory. The main result of this analysis is that the hump structure corresponds to a gap ratio of 3.5, and that large electron-point defect scattering is the main source of drastic reduction of the electronic thermal conductivity from that given by the usual Wiedeman–Franz law.     

Dephenolization,dearomatization and detoxification of olive mill wastewater with sonication combined with additives and radical scavengers

In this study, the effects of some additives [manganese (III) oxide (Mn₃O₄), Cu⁺², Fe⁰ and potassium iodate (KIO₃)] and some radical scavengers [sodium carbonate (Na₂CO₃), perfluorohexane (C₆F₁₄) and t-butyl alcohol (C₄H₁₀O)] on the sonication of olive mill effluent wastewater (OMW) were investigated since the wastewaters of this industry are removed with low efficiencies. The maximum total phenol and total aromatic amines (TAAs) removal efficiencies were 88% and 79%, respectively, at 60 °C with only 150 min sonication. The maximum phenol removal was found as 98% with 19 mg L⁻¹ perfluorohexane and 5 mg L⁻¹ Fe⁰ while the maximum TAAs removal was 99% with 16 mg L⁻¹ KIO₃. Catechol, tyrosol, quercetin, caffeic acid, 4-methyl catechol, 2-phenylphenol (2-PHE) and 3-phenyl phenol (3-PHE) were detected as phenol intermediates while trimethlyaniline, aniline, o-toluidine, o-anisidine, dimethylaniline, ethylbenzene and durene were identified as TAAs in the OMW. The maximum acute toxicity removals were 96% and 99% in Vibrio fischeri and Daphnia magna, respectively. Total phenol, TAAs and the toxicity in an OMW were removed efficiently and cost-effectively through sonication.     

Sequestration of some biogenic amines and poly(allyl)amine by high molecular weight polycarboxylic ligands in aqueous solution

The interactions of two high molecular weight polycarboxylic ligands [polyacrylic-co-maleic, MW = 70 kDa, and poly(methyl vinyl ether-co-maleic acid), MW = 15 kDa] with some polyamines [1,4-diaminobutane (or putrescine), histamine and poly(allyl)amine, MW = 15 kDa] were studied, at t = 25 °C and at low ionic strength (I = 0.015 mol L^? 1) by potentiometric measurements. For all investigated systems, the formation of (am)(L)H_i species was found (am = amine, L = polycarboxylic ligand, i = 1…4); the stability of polyammonium–polycarboxylate complexes is fairly high and the formation percentage of most species reaches ～ 90% in the experimental conditions (mmolar concentration of reactants). The dependence on temperature and ionic strength of the stability of polyamine–polycarboxylate species was studied using some semiempirical equations and enthalpy data for the protonation of both components. The sequestering ability of polyelectrolytes towards amines was modeled by a sigmoid Boltzman type equation and was defined by calculating the parameter pL₅₀ (the total ligand concentration, as ? log C_L, able to bind 50% of cation); this parameter gives an objective representation of this ability. The dependence of pL₅₀ on pH, ionic strength and temperature was studied too.     

The effect of Ag layer thickness on the properties of WO3/Ag/MoO3 multilayer films as anode in organic light emitting diodes

Transparent conductive WO₃/Ag/MoO₃ (WAM) multilayer electrodes were fabricated by thermal evaporation and the effects of Ag layer thickness on the optoelectronic and structural properties of multilayer electrode as anode in organic light emitting diodes (OLEDs) were investigated using different analytical methods. For Ag layers with thickness varying between 5 and 20 nm, the best WAM performances, high optical transmittance (81.7%, at around 550 nm), and low electrical sheet resistance (9.75 Ω/cm²) were obtained for 15 nm thickness. Also, the WAM structure with 15 nm of Ag layer thickness has a very smooth surface with an RMS roughness of 0.37 nm, which is suitable for use as transparent conductive anode in OLEDs. The current density?voltage?luminance (J?V?L) characteristics measurement shows that the current density of WAM/PEDOT:PSS/TPD/Alq₃/LiF/Al organic diode increases with the increase in thickness of Ag and WO₃/Ag (15 nm)/MoO₃ device exhibits a higher luminance intensity at lower voltage than ITO/PEDOT:PSS/TPD/Alq₃/LiF/Al control device. Furthermore, this device shows the highest power efficiency (0.31 lm/W) and current efficiency (1.2 cd/A) at the current density of 20 mA/cm², which is improved 58% and 41% compared with those of the ITO-based device, respectively. The lifetime of the WO₃/Ag (15 nm)/MoO₃ device was measured to be 50 h at an initial luminance of 50 cd/m², which is five times longer than 10 h for ITO-based device.     

Synthesis and electrical properties of nanocrystalline Ca1 − xEuxMnO3 ± δ (0.1 ≤ x ≤ 0.4) powders prepared at low temperature using citrate gel method

Nanopowders of Ca_1 − xEu_xMnO₃ (0.1 ≤ x ≤ 0.4) manganites were synthesized as a single phase using the auto gel-combustion method. The citrate method shows to be simple and appropriate to obtain single phases avoiding segregation or contamination. The Ca_1 − xEu_xMnO₃ system has been synthesized at 800 °C during 18 h, against the conventional method of mixing oxides used to obtain these materials at higher temperatures of synthesis. The formation reaction was monitored by X-ray diffraction (XRD) analysis and an infrared absorption technique (FTIR). The polycrystalline powders are characterised by nanometric particle size, ∼ 48 nm as determined from X-ray line broadening analysis using the Scherrer equation. Morphological analysis of the powders, using the scanning electron microscope (SEM), revealed that all phases are homogeneous and the europium-substituted samples exhibit a significant decrease in the grain size when compared with the undoped samples. The structure refinement by using the Rietveld method indicates that the partial calcium substitution by europium (for x ≥ 0.3) modifies the orthorhombic structure of the CaMnO₃ perovskite towards a monoclinic phase. All manganites show two active IR vibrational modes around 400 and 600 cm^− 1. The high temperature dependence of electrical resistivity (between 25 and 600 °C) allows us to conclude that all the samples exhibit a semiconductor behaviour and the europium causes a decrease in the electrical resistivity by more than one order of magnitude. The results can be well attributed to the Mn⁴⁺/Mn³⁺ ratio.     

Estimating the model-specific uncertainty of aircraft noise calculations

Aircraft noise contours are estimated with model calculations. Due to their impact, e.g., on land use planning, calculations need to be highly accurate, but their uncertainty usually remains unaccounted for. The objective of this study was therefore to quantify the uncertainty of calculated average equivalent continuous sound levels (L_Aeq) of complex scenarios such as yearly air operations, and to establish uncertainty maps. The methodology was developed for the simulation program FLULA2. In a first step, the partial uncertainties of modelling the aircraft as a sound source and of modelling sound propagation were quantified as a function of aircraft type and distance between aircraft and receiver. Then, these uncertainties were combined for individual flights to obtain the uncertainty of the single event level (L_AE) at a specified receiver grid. The average L_Aeq of a scenario results from the combination of the L_AE of many single flights, each of which has its individual uncertainties. In a last step, the uncertainties of all L_AE were therefore combined to the uncertainty of the L_Aeq, accounting also for uncertainties of the number of movements and of prognoses. Uncertainty estimations of FLULA2 calculations for Zurich and Geneva airports revealed that the standard uncertainty of the L_Aeq ranges from 0.5 dB (day) to 1.0 dB (night) for past-time scenarios when using radar data as input, and from 1.0 dB (day) to 1.3 dB (night) for future scenarios, in areas where L_Aeq ⩾ 53 dB (day) and L_Aeq ⩾ 43 dB (night), respectively. Different uncertainty values may result for other models and/or airports, depending on the model sophistication, traffic input data, available sound source data, and airport peculiarities such as the specific aircraft fleet or prevailing departure and arrival procedures. The methodology, while established for FLULA2 on Zurich and Geneva airports, may be applied to other models and/or airports, but the partial uncertainties have to be specifically re-established to account for individual models and underlying sound source data.     

Oxygen-rich Ti1−xO2 pillar growth at a gold nanoparticle–TiO2 contact by O2 exposure

In-situ gas-injection transmission electron microscopy revealed that a pillar grew at the edge of the interface of a gold nanoparticle and a TiO₂ substrate during exposure to O₂ gas at 100 Pa. The pillar was found to have a titanium-deficient chemical composition of Ti_1 ? xO₂ (x > 0) by electron energy loss spectroscopy (EELS). The spectra showed a chemical shift of oxygen and titanium ions to have ionic states of Ti³⁺ and O^y? (y < 3/2). The formation of the Ti_1 ? xO₂ at the contact edge of gold–Ti_1 ? xO₂ interface is discussed from the perspective of an O₂ affinity, which plays an important role in CO oxidation process of supported gold particle.     

Development and characteristics of solenoid-type SMD RF chip inductors

Simple, solenoid-type surface-mounted device (SMD) chip inductors utilizing low-loss Al₂O₃ core materials for a radio-frequency (RF) drive microwave circuit application were developed. The SMD chip inductors were fabricated with five different specifications, namely, 0.86 × 0.46 × 0.45, 1.0 × 0.5 × 0.5, 1.5 × 1.0 × 0.7, 2.1 × 1.5 × 1.0, and 2.4 × 2.0 × 1.4 mm³. Copper coils with diameters in the range of 27–40 μm were used. The frequency characteristics of the inductance (L), quality factor (Q), and impedance of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with HP16193A test fixture). It was observed that the developed inductors with the number of turns of 12 have L of 34–270 nH, exhibit a self-resonant frequency (SRF) of 3.7–0.75 GHz, and have Q of 40–70 over the frequency ranges of 200 MHz–1.2 GHz. The L of inductors increases and the SRF decreases with increasing the size of inductors. From the experimental results, it was concluded that the high-frequency data calculated from the equivalent circuit and the derived equation of Q described quite well the experimental data of the developed inductors.