Liquid salt cooled flexible conversion ratio fast reactor: Neutronic design

This paper presents the neutronic design of a liquid salt cooled fast reactor with flexible conversion ratio. The main objective of the design is to accommodate interchangeably within the same reactor core alternative transuranic actinides management strategies ranging from pure burning to self-sustainable breeding. Two, the most limiting, core design options with unity and zero conversion ratios are described. Ternary, NaCl-KCl-MgCl2 salt was chosen as a coolant after a rigorous screening process, due to a combination of favourable neutronic and heat transport properties. Large positive coolant temperature reactivity coefficient was identified as the most significant design challenge. A wide range of strategies aiming at the reduction of the coolant temperature coefficient to assure self-controllability of the core in the most limiting unprotected accidents were explored. However, none of the strategies resulted in sufficient reduction of the coolant temperature coefficient without significantly compromising the core performance characteristics such as power density or cycle length. Therefore, reactivity control devices known as lithium thermal expansion modules were employed instead. This allowed achieving all the design goals for both zero and unity conversion ratio cores. The neutronic feasibility of both designs was demonstrated through calculation of reactivity control and fuel loading requirements, fluence limits, power peaking factors, and reactivity feedback coefficients. © 2009 Elsevier B.V. All rights reserved.

Characterization of the surface acoustic wave devices based on ZnO/nanocrystalline diamond structures

Nanocrystalline ZnO films with strong (0002) texture and fine grains were deposited onto ultra-nanocrystalline diamond (UNCD) layers on silicon using high target utilization sputtering technology. The unique characteristic of this sputtering technique allows room temperature growth of smooth ZnO films with a low roughness and low stress at high growth rates. Surface acoustic wave (SAW) devices were fabricated on ZnO/UNCD structure and exhibited good transmission signals with a low insertion loss and a strong side-lobe suppression for the Rayleigh mode SAW. Based on the optimization of the layered structure of the SAW device, a good performance with a coupling coefficient of 5.2% has been realized, promising for improving the microfluidic efficiency in droplet transportation comparing with that of the ZnO/Si SAW device. An optimized temperature coefficient of frequency of -23.4 ppm°C-1 was obtained for the SAW devices with the 2.72 μm-thick ZnO and 1.1 μm-thick UNCD film. Significant thermal effect due to the acoustic heating has been redcued which is related to the temperature stability of the ZnO/UNCD SAW device. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Physico-chemical properties of alkaline phosphatases released by a planktonic crustacean, Daphnia magna (Cladocera)

Our studies investigated the physico-chemical properties of alkaline phosphatase excreted by D. magna. This cladoceran mainly released alkaline phosphatase, though it also released a small amount of acid phosphatase. The alkaline phosphatase showed a broad pH optimum (8.05-10.0), and had a broad optimum temperature (30-35 degrees C) with a temperature coefficient (Q(10)) of 2.45. The K-m of the enzyme is 0.15 +/- 0.02 mM when p-nitrophenyl phosphate is used as a substrate, and the V-max is 0.43 +/- 0.01 mu M pNP mg(-1) DW h(-1). Even though alkaline phosphatase had been incubated in chloroform saturated with WC medium for 13 days, its activity was 54% that of the original. The enzyme was strongly inactivated by EDTA, and appeared to be zinc dependent. The alkaline phosphatase activity remained constant when D. magna was fed different quantities of Chlorella sp. The sensitivity of D. magna phosphatase activity to phosphate was time-dependent. During the first 16 hrs, the enzyme was insensitive to phosphate addition, after 24 hrs incubation the enzyme became sensitive to phosphate addition.

Design consideration and performance of high-power and high-brightness InGaAs-InGaAsP-AlGaAs quantum-well diode lasers (lambda=0.98 mu m)

In this paper, we conduct a theoretical analysis of the design, fabrication, and performance measurement of high-power and high-brightness strained quantum-well lasers emitting at 0.98 mum, The material system of interest consists of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. Some key parameters of the laser structure are theoretically analyzed, and their effects on the laser performance are discussed. The laser material is grown by metal-organic chemical vapor deposition and demonstrates high quality with low-threshold current density, high internal quantum efficiency, and extremely low internal loss. High-performance broad-area multimode and ridge-waveguide single-mode laser devices are fabricated. For 100-mum-wide stripe lasers having a cavity length of 800 mum, a high slope efficiency of 1.08 W-A, a low vertical beam divergence of 34 degrees, a high output power of over 4.45 W, and a very high characteristic temperature coefficient of 250 K were achieved. Lifetime tests performed at 1.2-1.3 W (12-13 mW/mum) demonstrates reliable performance. For 4-mum-wide ridge waveguide single-mode laser devices, a maximum output power of 394 mW and fundamental mode power up to 200 mW with slope efficiency of 0.91 mW/mum are obtained.

High-performance 980-nm quantum-well lasers using a hybrid material system of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers grown by metal-organic chemical vapor deposition

We report on the material growth and fabrication of high-performance 980-nm strained quantum-well lasers employing a hybrid material system consisting of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in flexibility of laser design, simple epitaxial growth, and improvement of surface morphology and laser performance. The as-grown InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.95 eV) lasers achieve a low threshold current density of 150 A/cm(2) (at a cavity length of 1500 mu m), internal quantum efficiency of similar to 95%, and low internal loss of 1.8 cm(-1). Both broad-area and ridge-waveguide laser devices are fabricated. For 100-mu m-wide stripe lasers with a cavity length of 800 Irm, a slope efficiency of 1.05 W/A and a characteristic temperature coefficient (T-0) of 230 K are achieved. The lifetime test demonstrates a reliable performance. The comparison with our fabricated InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.87 eV) lasers and Al-free InGaAs-InGaAsP (1.6 eV)-InGaP lasers are also given and discussed. The selective etching between AlGaAs and InGaAsP is successfully used for the formation of a ridge-waveguide structure. For 4-mu m-wide ridge-waveguide laser devices, a maximum output power of 350 mW is achieved. The fundamental mode output power can be up to 190 mW with a slope efficiency as high as 0.94 W/A.

980nm InGaAs/InGaAsP quantum well lasers with AlGaAs cladding grown by metal organic chemical vapour deposition

The authors report on the fabrication of 980 nm InGaAs strained quantum well lasers with hybrid materials of InGaAsP as waveguide and AlGaAs as cladding grown by metal organic chemical vapour deposition. The InGaAs/InGaAsP/AlGaAs diode lasers (100 x 800 mu m) with broadened waveguide structure exhibit a threshold current of 180 mA, a slope efficiency of 1.0 W/A, and a high characteristic temperature coefficient (T-0) of 230 K.

Growth and fabrication of high performance 980nm strained InGaAs quantum well lasers using novel hybrid material system of InGaAsP and AlGaAs

In this paper, we report on the design, growth and fabrication of 980nm strained InGaAs quantum well lasers employing novel material system of Al-free active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in laser structure design, improvement of surface morphology and laser performance. We demonstrate an optimized broad-waveguide structure for obtaining high power 980nm quantum well lasers with low vertical beam divergence. The laser structure was grown by low-pressure metalorganic chemical vapor deposition, which exhibit a high internal quantum efficiency of similar to 90% and a low internal loss of 1.5-2.5 cm(-1). The broad-area and ridge-waveguide laser devices are both fabricated. For 100 mu m wide stripe lasers with cavity length of 800 mu m, a low threshold current of 170mA, a high slope efficiency of 1.0W/A and high output power of more than 3.5W are achieved. The temperature dependences of the threshold current and the emitting spectra demonstrate a very high characteristic temperature coefficient (T-o) of 200-250K and a wavelength shift coefficient of 0.34nm/degrees C. For 4 mu m-width ridge waveguide structure laser devices, a maximum output power of 340mW with GOD-free thermal roll-over characteristics is obtained.

Synergistic extraction of zinc(II) with mixtures of CA-100 and cyanex 272

The extraction of zinc(II) from an aqueous chloride medium has been studied using mixtures of sec-nonylphenoxy acetic acid (CA-100) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272). The results demonstrate that zinc ion is extracted into heptane as ZnA(2).2HA with CA-100, ZnL2.2HL with Cyanex 272, and ZnA(2)L(2)H(2) with synergistic mixture. The equilibrium constants of the these species have been calculated and extraction mechanisms have been proposed. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of extractability. The synergistic system enhances the extraction efficiency of zinc(II) and also improves the selectivity between zinc(II) and cadmium(II).

LDPE/carbon black conductive composites: Influence of radiation crosslinking on PTC and NTC properties

The electrical resistivity of low-density polyethylene/carbon black composites irradiated by Co-60 gamma-rays was investigated as a function of temperature. The experimental results obtained by scanning electron microscopy, solvent extraction techniques, and pressure-specific volume-temperature analysis techniques showed that the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects of the composites were influenced by the irradiation dose, network forming (gel), and soluble fractions (Sol). The NTC effect was effectively eliminated when the radiation dose reached 400 kGy. The results showed that the elimination of the NTC effect was related to the difference in the thermal expansion of the gel and Sol regions. The thermal expansion of the sol played an important role in both increasing the PTC intensity and decreasing the NTC intensity at 400 kGy.

Studies on the PTC/NTC effect of carbon black filled low density polyethylene composites

The positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effect of carbon black (CB) filled low density polyethylene (LDPE) composites was studied using electrical resistivity spectra, DSC, tensile mechanical analysis (TMA) and small-angle X-ray scattering (SAXS) techniques. The three LDPEs used have a similar crystallinity and different melting index (MI). The experimental results indicate that the CB has no significant effect on the crystallinity and the long spacing of crystalline domains of LDPE. Based upon the TMA and dynamic elastic modulus spectra, it can be concluded that the PTC effect is related to the thermal expansion of the polymer matrix, and the NTC effect is caused by a decrease of the elastic modulus of the polymer at high temperatures. The NTC effect can be reduced by enhancing either the elastic modulus or the interaction between carbon black and matrix. (C) 1997 Elsevier Science Ltd.

Electrical and dynamic mechanical behavior of carbon black filled polymer composites

The effect of processing conditions on the electrical and dynamic behavior of carbon black (CB) filled ethylene/ethylacrylate copolymer (EEA) composites was investigated. The compounds were prepared by two methods, solution blending and mechanical mixing. Compared with the solution counterpart, the mechanical composites have a strong positive temperature coefficient (PTC) effect and a high dynamic elastic modulus, which results from the good dispersion state of carbon black in EEA, i.e. the strong interaction between carbon black and EEA. It can be concluded that the strong interaction between polymer and carbon black is essential for composites to have a high PTC intensity, good electrical reproducibility and high dynamic elastic modulus. Copyright (C) 1996 Published by Elsevier Science Ltd.

THE OPTICAL AND ELECTRICAL-PROPERTIES OF DYSPROSIUM AND YTTERBIUM MONOPHOSPHIDES

Dysprosium and ytterbium monophosphides have been prepared by the solid state reaction. The optical and electrical properties have been studied. Evidence that DyP and YbP are semiconductors has been obtained from the study of the absorption spectrum, the negative temperature coefficient of resistance and the rectifying effect. Their energy gaps are determined as 1.15 eV for DyP and 1.30 eV for YbP, electric conduction type is n-type, resistivities are about 10(-2) ohm cm and Hall mobility is 8.5-80 cm2/Vs. The p-n junction is formed on the LnP/Si.

Non-linear electronic transport in Pt nanowires deposited by focused ion beam

Electrical transport and structural properties of platinum nanowires, deposited using the focussed ion beam method have been investigated. Energy dispersive X-ray spectroscopy reveals metal-rich grains (atomic composition 31% Pt and 50% Ga) in a largely non-metallic matrix of C, O and Si. Resistivity measurements (15-300 K) reveal a negative temperature coefficient with the room-temperature resistivity 80-300 times higher than that of bulk Pt. Temperature dependent current-voltage characteristics exhibit non-linear behaviour in the entire range investigated. The conductance spectra indicate increasing non-linearity with decreasing temperature, reaching 4% at 15 K. The observed electrical behaviour is explained in terms of a model for inter-grain tunnelling in disordered media, a mechanism that is consistent with the strongly disordered nature of the nanowires observed in the structure and composition analysis.

A Lead-Free and High-Energy Density Ceramic for Energy Storage Applications

In this work, we demonstrate a very high-energy density and high-temperature stability capacitor based on SrTiO3-substituted BiFeO3 thin films. An energy density of 18.6 J/cm3 at 972 kV/cm is reported. The temperature coefficient of capacitance (TCC) was below 11% from room temperature up to 200°C. These results are of practical importance, because it puts forward a promising novel and environmentally friendly, lead-free material, for high-temperature applications in power electronics up to 200°C. Applications include capacitors for low carbon vehicles, renewable energy technologies, integrated circuits, and for the high-temperature aerospace sector. © 2013 Crown copyright

Barrier characteristics of PtSi/p-Si schottky diodes as determined from I-V-T measurements

The current-voltage-temperature characteristics of PtSi/p-Si Schottky barrier diodes were measured in the temperature range 60-115 K. Deviation of the ideality factor from unity below 80 K may be modelled using the so-called T-0 parameter with T-0 = 18 K. It is also shown that the curvature in the Richardson plots may be remedied by using the flatband rather than the zero-bias saturation current density. Physically, the departure from ideality is interpreted in terms of an inhomogeneous Schottky contact. Here we determine a mean barrier height at T = 0 K, phi(b)(-0) = 223 mV, with an (assumed) Gaussian distribution of standard deviation sigma(phi) = 12.5 mV. These data are correlated with the zero-bias barrier height, phi(j)(0) = 192 mV (at T = 90 K), the photoresponse barrier height, phi(ph) = 205 mV, and the flatband barrier height, phi(fb) = 214 mV. Finally, the temperature coefficient of the flatband barrier was found to be -0.121 mV K-1, which is approximately equal to 1/2(dE(g)(i)/dT), thus suggesting that the Fermi level at the interface is pinned to the middle of the band gap.