A study of cross-gas-flow to stabilize an atmospheric pressure glow plasma in a multi-pin-to-multi-cupped-plane negative corona discharge

In a multi-pin-to-multi-cupped-plane DC negative corona discharge configuration, a stable and diffuse glow discharge controlled by a fast airflow was obtained. This paper investigates the effect of the air gas flow velocity and the electrode structure on the discharge mode transition and the stabilization of the glow discharge by means of electric measurements and emission records. The stabilization mechanism of the glow discharge is discussed. The maximum glow discharge current reached 3.9 mA and the average current density was about 0.7 mA/cm².     

Surface treatment of CFRP composites using femtosecond laser radiation

In the present work, we investigate the surface treatment of carbon fiber-reinforced polymer (CFRP) composites by laser ablation with femtosecond laser radiation. For this purpose, unidirectional carbon fiber-reinforced epoxy matrix composites were treated with femtosecond laser pulses of 1024 nm wavelength and 550 fs duration. Laser tracks were inscribed on the material surface using pulse energies and scanning speeds in the range 0.1–0.5 mJ and 0.1–5 mm/s, respectively. The morphology of the laser treated surfaces was investigated by field emission scanning electron microscopy. We show that, by using the appropriate processing parameters, a selective removal of the epoxy resin can be achieved, leaving the carbon fibers exposed. In addition, sub-micron laser induced periodic surface structures (LIPSS) are created on the carbon fibers surface, which may be potentially beneficial for the improvement of the fiber to matrix adhesion in adhesive bonds between CFRP parts.     

Design of hybrid photonic crystal fiber: Polarization and dispersion properties

A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm⁻¹ at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10⁻² at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.     

Low temperature synthesis of layered LiNiO2 cathode material in air atmosphere by ion exchange reaction

The layered LiNiO₂ cathode material for lithium ion battery was synthesized by ion-exchange reaction at low temperature in air atmosphere. The influence of synthesis conditions on the electrochemical performance of the resulting LiNiO₂ was investigated. The LiNiO₂ samples were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and infrared (IR) analysis. The results indicate that low temperature fabricated LiNiO₂ powders keep a single layered hexagonal structure and homogenous spheric shape like the raw material NiOOH. Charge and discharge tests show that the resultant LiNiO₂ exhibits good electrochemical properties. The first charge and discharge capacities of the sample are 183.4 mA h g^− 1 and 169.5 mA h g^− 1 at 0.5 mA cm^− 2, respectively. Galvanic charge/discharge and cyclic voltammetry tests reflect that LiNiO₂ electrode exhibits good cycle reversibility.     

Segments of a commercial Ge-doped optical fiber as a thermoluminescent dosimeter in radiotherapy

Optical fibers have been proposed as dosimeters in both diagnostic and radiotherapy applications. A commercial germanium (Ge)-doped silica fiber with a 50 μm core diameter which showed good thermoluminescence (TL) properties was selected for this study. The radiation sources used were a high dose rate brachytherapy iridium-192, MV photon and MeV electron beams from a linear accelerator. The coating of the fiber was chemically removed and then annealed at 400 °C for 1 h prior to irradiation. After irradiation, the fiber was read on a Harshaw Model 3500 TLD reader. The optical fiber had one well-defined glow peak at 327 ± 2 °C at all the radiotherapy energies. The dose response was linear within the clinical relevant dose for all these energies. Reproducibility was mainly within 4–6% (one standard deviation) for high energy photons and electrons. The fiber was found to be energy independent within the MV photon energy range. At room temperature the fading up until 1 month was around 6% which was within the 6% uncertainty of the sensitivity calibration of the fiber. Re-using the fiber four times did not significantly alter the sensitivity factor. The optical fiber was found to be dose rate as well as angular independent. Central axis depth dose curves of both 10 MV photons and 12 MeV electrons using the fiber showed relatively good agreement to standard depth dose curves in water within 4%. The Ge-doped fiber is a promising TL dosimeter but improvements have to be made to reduce the reproducibility within 3% for high energy photons and electrons.     

Preparation of carbon nanoparticles from electrolysis of molten carbonates and use as anode materials in lithium-ion batteries

The electrochemical reduction of molten Li–Na–K carbonates at 450 °C provides “quasi-spherical” carbon nanoparticles with size comprised between 40 and 80 nm (deduced from AFM measurements). XRD analyses performed after washing and heat-treatment at various temperatures have revealed the presence of graphitised and amorphous phases. The d₀₀₂ values were close to the ideal one obtained for pure graphite. Raman spectroscopy has pointed out surface disordering which increases with increasing temperature of the heat-treatment. The presence of Na and Li on the surface of the carbon powder has been evidenced by SIMS. The maximum Na and Li contents were observed for carbon samples heat-treated at 400 °C. Their electrochemical performances vs. the insertion/deinsertion of lithium cations were studied in 1 M LiPF₆–EC : DEC : DMC (2 : 1 : 2). The first charge–discharge cycle is characterised by a high irreversible capacity as in the case of hard-disordered carbon materials. However, the potential profile in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon: rather continuous charge–discharge curves sloping between 1.5 and 0.3 V vs. Li / Li⁺, and successive phase transformations between 0.3 and 0.02 V vs. Li / Li⁺. The best electrochemical performances were obtained with carbon powders heat-treated at 400 °C which exhibits a reversible capacity value of 1080 mAh g^− 1 (composition of Li_2.9C₆). This sample has also both the lowest surface disordering (deduced from Raman spectroscopy), and the highest Na and Li surface contents (deduced from SIMS).     

Ultra-broad and flat supercontinuum generation in short photonic crystal fiber combined with conventional fibers

In order to gain ultra-broad and flat super-continuum (SC) spectrum, we propose and demonstrate a new scheme. By coupling a train of short pulses with 100 fs width and 16.2 mW average power generated by a mode-locked laser into the scheme – short photonic crystal fiber (PCF) combined with conventional fibers. The SC spectrum has 491 nm bandwidth at −15 dBm below the spectral peak with ±0.5 dBm uniformity 100 nm in only 0.45 m PCF. The spectral bandwidth generated in the scheme increases 292 nm than spectrum generated in the two conventional fibers, and increases 152 nm than spectrum generated in the three convention fibers.     

A simple dye-sensitized solar cell sealing technique using a CO2 laser beam excited by 60 Hz AC discharges

Dye-sensitized solar cells (DSSCs) use two glass substrates (photo electrode and counter electrode) coated with fluorine-doped tin oxide (FTO) to harvest light into the cell and to collect electrons. The space between the photo electrode and the counter electrode are filled with a liquid type electrolyte for electron transfer into the cell. Therefore, an appropriate sealing method is required to prevent the liquid electrolyte leaking out. In this paper, a simple CO₂ laser beam with TEM₀₀ mode excited by a 60 Hz AC discharge was used to seal two glass substrates coated with FTO for the fabrication of DSSCs. The sealing technique improved the durability and stability of the DSSCs. The optimal conditions for the sealing of the DSSCs are related to the pin-hole diameter, the discharge current and the moving velocity of the target. Especially, the CO₂ laser beam is used as a heat source that is precisely controlled by the pin-hole, which plays an important role in adjusting its spot size. From these results, the maximum laser power was found to be 40 W at 18 Torr and 35 mA. In order to achieve the best sealing quality, the following parameters are required: a pin-hole diameter of 4 mm, input voltage of 10.73 kV, discharge current of 9.31 mA, moving velocity of 1 mm/s and distance from the target surface of 26.5 cm. Scanning electron microscope images show that the sealing quality obtained using the CO₂ laser beam is superior to that obtained using a hot press or soldering iron.     

The synthesis and properties of nanocrystalline electrode materials by mechanical alloying

In this work, we have experimentally studied the structure and electrochemical properties of nanocrystalline TiFe- and LaNi₅-type alloys. These materials were prepared by mechanical alloying (MA) followed by annealing. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the respective replacement of Fe in TiFe by Ni and/or by Cr, Co, Mo, Zr improved not only the discharge capacity but also the cycle life of these electrodes. In the nanocrystalline TiFe_0.25Ni_0.75, powder discharge capacity up to 155 mA h g⁻¹ was measured (at 40 mA g⁻¹ discharge current). On the other hand, a partial substitution of Ni by Al or Mn in LaNi_5−xM_x alloy leads to an increase in discharge capacity. The alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacity up to 258 mA h g⁻¹ was measured (at 40 mA g⁻¹ discharge current). The studies show, that electrochemical properties of Ni–MH batteries are the function of the microstructure and the chemical composition of used electrode materials.     

Carbon nanostructures synthesized by arc discharge between carbon and iron electrodes in liquid nitrogen

An idea of using pure iron and graphite electrodes was employed for synthesizing carbon nanoparticles by arc discharge in liquid nitrogen. The synthesized products consist of multiwalled carbon nanotubes (MW–CNT), carbon nanohorns (CNH), and carbon nanocapsules (CNC) with core–shell structure. Effect of metallic cathode and discharge current on product structure and yield had been experimentally investigated. Typical evidence of transmission electron microscopic images revealed that under some certain conditions of discharge in liquid nitrogen the synthesized products mainly consisted of CNCs with mean diameter of 50–400 nm. When conventional graphitic electrodes were employed, CNHs with some MW–CNTs were mainly synthesized. Meanwhile, MW–CNTs with diameter of 8–25 nm and length 150–250 nm became less selectively synthesized as cathode deposit under the condition of discharge in liquid nitrogen with higher arc current. The production yield of carbon nanoparticles synthesized by either carbon–carbon or carbon–iron electrodes became also lower with an increase in the arc current.     

Gamma radiation effects on the DPB SFS in space FOGs applications

Superfluorescent fiber source (SFS) is generally considered to be promising in optical sensing. In this paper, the gamma radiation effect on the double pass backward (DPB) SFS was investigated. Firstly, a sample of DPB SFS together with a 9 m Er-doped fiber (EDF) was irradiated by ⁶⁰Co source with radiation dose rate of 3.6 Gy/h and total dose of 200 Gy. And the results were analyzed to find that at the very start of radiation the RIL of the sampled Er-doped fiber was greater than that of sampled SFS while at about 100 Gy the RIL slope of the EDF became less than that of the SFS. Above all, the loss from EDF was dominant to that from the SFS in gamma radiation environment. Mean wavelength of the SFS drifted about 4 nm mainly caused by the radiation loss. In the end, the potential influence to FOGs in space applications was simulated.     

Fabrication of thin-film transistor based on self-assembled single-walled carbon nanotube network

Thin-film transistor based on controllable electrostatic self-assembled monolayer single-wall carbon nanotubes (SWNTs) network has been fabricated by varying the density of nanotubes on the silicon substrate. The densities of SWNTs network have been investigated as a function of concentration and assembly time. It has been observed that the density of SWNTs network increases from 0.6 µm⁻² to 2.1 µm⁻², as the average on-state current (I_on) increases from 0.5 mA to 1.47 mA. The device has a current on/off ratio (I_on/I_off) of 1.3×10⁴ when I_on reaches to 1.34 mA.     

Optical fiber strain and temperature sensor based on an in-line Mach–Zehnder interferometer using thin-core fiber

We propose and demonstrate a fiber in-line Mach–Zehnder interferometer using thin-core fibers. This in-line interferometer is composed of a short section of thin-core fiber inserted between two single mode fibers (SMF), and demonstrated as a strain and temperature sensor in this study. A strain sensitivity of ?1.83 pm/με with a measurement range of 0?2000 με, and the temperature sensitivity of ?72.89 pm/°C with a temperature variation of 50 °C are achieved. We also discussed that the influence of strain and temperature change on the relative power ratios among the excited cladding modes in thin-core fibers.     

Mixed oxygen ion and electron conducting hollow fiber membranes for oxygen separation

Phase inversion spinning technique was employed to prepare dense perovskite hollow fiber membranes made from composition BaCo_xFe_yZr_zO_3−δ (BCFZ, x + y + z = 1.0). Scanning electron microscope (SEM) shows that such hollow fibers have an asymmetric structure, which is favored to the oxygen permeation. An oxygen permeation flux of 7.6 cm³/min cm² at 900 °C under an oxygen gradient of 0.209 × 10⁵ Pa/0.065 × 10⁵ Pa was achieved. From the Wagner Theory, the oxygen permeation through the hollow fiber membrane is controlled by both bulk diffusion and surface exchange. The elements composition of fresh fiber and the fiber after long-term experiments were analyzed by energy-dispersive X-ray spectra (EDXS). Compared to the fresh fiber, sulphur was found on the tested hollow fiber membrane surface exposed to the air side and in the bulk, and Ba segregations occur on the tested hollow fiber membrane surface exposed to the air side. A decrease of the oxygen permeation flux was observed, which was probably due to the sulphur poisoning.     

High speed ultra short pulse fiber ring laser using photonic crystal fiber nonlinear optical loop mirror

A scheme to generate high speed optical pulse train with ultra short pulse width is proposed and experimentally studied. Two-step compression is used in the scheme: 20 GHz and 40 GHz pulse trains generated from a rational harmonic actively mode-locked fiber ring laser is compressed to a full width at half-maximum (FWHM) of ~ 1.5 ps using adiabatic soliton compression with dispersion shifted fibers (DSF). The pulse trains then undergo a pedestal removal process by transmission through a cascaded two photonic crystal fiber (PCF)-nonlinear optical loop mirrors (NOLM) realized using a double-ring structure. The shortest output pulse width obtained was ~ 610 fs for 20 GHz pulse train and ~ 570 fs for 40 GHz pulse train. The signal to noise ratio of the RF spectrum of the output pulse train is larger than 30 dB. Theoretical simulation of the NOLM transmission is conducted using split-step Fourier method. The results show that two cascaded NOLMs can improve the compression result compared to that for a single NOLM transmission.     

Studies of dielectric relaxation in natural fiber–polymer composites

Polymer composites of a polyester resin matrix filled with short palm tree lignocellulosic fibers were studies by means of dielectric spectroscopy in the frequency range 0, 1–100 kHz and temperature interval from 40 °C to 200 °C. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial relaxation that is attributable to the accumulation of charges at the Palm fibers/polyester interfaces.     

Inorganic species formation in a discharged water generating system

Inorganic species formation in a discharged water generating (DWG) system consisting of a plane-to-plane electrode arrangement with a 20 kV, 20 mA and 1 kHz power source has been investigated. The DWG system is able to produce the various oxidants HNO₂, HNO₃ and O₃, as well as OH radicals and many other unconfirmed radicals. These products can play an important role in the advanced oxidation of organic compounds and in rot protection. The pH of water discharged from the system for 20 min during inflow of natural air was about 3, nitrogen concentrations of nitrite and nitrate were 4.6 mg/L and 7.9 mg/L, respectively, residual dissolved ozone concentration was 0.7 mg/L and the oxidation power as measured by KI titration methods was approximately equivalent to 46 mg-O₃/L.     

A new cross-protection dual-WDM-PON architecture with carrier-reuse colorless ONUs

This paper proposes a new cross-protection colorless dual-WDM-PON architecture. The proposed protection scheme can provide 1 + 1 downstream protection and 1:1 upstream protection against both feeder fiber and distribution fiber failures by using the fiber links and AWGs of the neighboring WDM-PON. Wavelength is reused for the down- and up-stream transmissions in dual-WDM-PONs where gain-saturated reflective semi-conductor optical amplifiers (RSOAs) are employed as colorless transmitters in ONUs. The number of extra protection fibers is minimized and wavelength is much more efficiently utilized compared with other protection schemes. The feasibility and operation of the proposed dual-WDM-PON architecture are experimentally verified with 1.25 Gb/s for upstream and 2.5 Gb/s for downstream over 20 km single mode fiber transmission in both working and protection modes.     

Structural and electrochemical properties of LiNi0.5Mn0.5 − xAlxO2 (x = 0, 0.02, 0.05, 0.08, and 0.1) cathode materials for lithium-ion batteries

Layered LiNi_0.5Mn_0.5 ? xAl_xO₂ (x = 0, 0.02, 0.05, 0.08, and 0.1) series cathode materials for lithium-ion batteries were synthesized by a combination technique of co-precipitation and solid-state reaction, and the structural, morphological, and electrochemical properties were examined by XRD, FT-IR, XPS, SEM, CV, EIS, and charge–discharge tests. It is proven that the aliovalent substitution of Al for Mn promoted the formation of LiNi_0.5Mn_0.5 ? xAl_xO₂ structures and induced an increase in the average oxidation number of Ni, thereby leading to the shrinkage of the lattice volume. Among the LiNi_0.5Mn_0.5 ? xAl_xO₂ materials, the material with x = 0.05 shows the best cyclability and rate ability, with discharge capacities of 219, 169, 155, and 129 mAh g^? 1 at 10, 100, 200, and 400 mA g^? 1 current density respectively. Cycled under 40 mA g^? 1 in 2.8–4.6 V, LiNi_{0. 5}Mn_0.45Al_0.05O₂ shows the highest discharge capacity of about 199 mAh g^? 1 for the first cycle, and 179 mAh g^? 1 after 40 cycles, with a capacity retention of 90%. EIS analyses of the electrode materials at pristine state and state after first charge to 4.6 V indicate that the observed higher current rate capability of LiNi_{0. 5}Mn_0.45Al_0.05O₂ can be understood due to the better charge transfer kinetics.     

Reduction of nonlinear impairments in fiber transmission system using fiber and/or transmitter diversity

A multi-fiber architecture is proposed to mitigate the nonlinear impairments in fiber-optic systems. The power launched to each fiber is reduced in multi-fiber architecture as compared to the case of single fiber leading to reduction in nonlinear impairments. The optical pulses propagating in the fibers undergo different amount of phase shifts and timing delays. Optical and electrical equalization techniques to compensate for these channel effects are discussed. Our numerical simulation results show that for unrepeatered systems, the performance (Q factor) is improved by 6.2 dB using 8-fiber configuration as compared to single-fiber system. In addition, for multi-span system, the transmission reach at a bit error rate (BER) of 2.1 × 10^? 3 is quadrupled in 8-fiber configuration.