High speed quantum key distribution system

Quantum key distribution (QKD) systems can generate unconditionally secure common key between remote users. Improvement of QKD performance, particularly on key generation rate, has been required to meet current network traffic. The present paper considers system requirement to improve key generation rate by increasing photon detection rate and reducing error rate. A high-speed QKD system should be equipped with low loss receivers with high visibility, highly efficient photon detectors with small dark count probability, and a stable clock synchronization system with low stray light to the quantum signals. A solution for these issues are given by employing planar lightwave circuit interferometers, single photon detection circuits and modules, and clock synchronization based on wavelength division multiplexing (WDM) technique. A QKD system has been developed by combining these techniques. The system working with 625 MHz clock generated sift key at the rate of 2.4 kbps through a 97-km single installed fiber core.     

Characteristics of the Beam-Steerable Difference-Frequency Generation of Terahertz Radiation

We have investigated the characteristics of a terahertz (THz) beam steering method based on a combination of difference-frequency generation (DFG) with the principle of the phased array antenna. In the DFG of THz radiation from a nonlinear optical crystal pumped by optical beams, the phase front of the THz radiation is indirectly tilted by adjusting the relative incidence angle between the pump beams to the crystal. A magnification of the steering angle with a factor of 193 is demonstrated as the most important effect provided by the method. The effect allows the use of a high-speed optical deflector for adjusting the incidence angle, accelerating the steering more than a hundred times compared with mechanical methods. The phase mismatching between the THz radiation and the pump beams as well as the refraction at the crystal surface limit the steering angle of the THz radiation to 56°, full width at half maximum.     

Melting and precision casting of Ti-6Al-4V alloy by use of electron beam furnace

For melting and casting of Ti-6Al-4V alloy by use of an electron beam furnace, key technologies have been developed: measurement and control of temperature, amount, and chemical composition of molten pool. Temperature in the molten pool was measurred by applying three devices; a thermocouple, a two color pyrometer and the rate of vaporization from the molten pool. Temperature measured by an optical pyrometer without influence of plasma by shifting the wave lengths of the light for the optical pyrometry from those of plasma evolved above the molten pool was in a good accordance with that estimated from the vaporization rate. By combining temperatures measured by three methods, the temperature gradient in the molten pool was estimated to be a level of 100 K/cm. In order to derive an empirical equation for the depth of molten pool of various metals, the depth of the molten pool was determined for Ti, Ti-6Al-4V alloy, solar grade Si, low carbon steel, and stainless steel by chemical etching of vertical cross section of an ingot melted and solidified in a skull crucible. Chemical compositions of Ti-6Al-4V alloy melt before casting was adjusted by adding an aluminum block into the pool before pouring, which compensated vaporization loss of Al from the pool surface under high vacuum. Since, a key to settle Al content in the specified range is the yield and distribution of Al in every castparts, influences of operating variables on the yield have been studied by paying attention to rapid temperature change observed immediately after addition of aluminum. Formerly Graduate School of Iron and Steel Technology Pohang University of Science and Technology San 31 Hyoja-dong, Nam-gu, Pohang 790-784, Korea     

Effects of intensity of incident light and concentrations of Synechococcus sp. and 2-hydroxy-1,4-naphthoquinone on the current output of photosynthetic electrochemical cell

We examined the effects of the intensity of incident light and the concentrations of cyanobacterium, Synechococcus sp. UTEX2380, and an electron transfer mediator, 2-hydroxy-1,4-naphthoquinone (HNQ), on the current output of a photosynthetic electrochemical cell operated under illumination. Though the current density was higher with increasing concentration of Synechococcus sp., increase in the current density was suppressed at more than 24 μg chlorophyll/ml. The current density reached a maximum value at 1 mM HNQ. The current density was saturated at 50 W/m² probably due to reoxidation of HNQ by oxygen photosynthetically evolved. The conversion efficiency of light energy to electrical energy was 3.3%. For the analysis of energy loss for four steps in the electrochemical cell reaction, the energy loss remarkably arose from the reaction of the electron transfer chain and the high internal resistance of the electrochemical cell.     

Study on presence/absence of central nervous tissues as BSE specified risk material in processed and raw meat products in Japan

Various countries including Japan issued the complete removal of brain and spinal cord (SC) tissues from meat products due to BSE risk factor. In this study using commercially available Ridascreen^® risk material test kit, we tried to evaluate the efficiency of removing specific risk material (SRM) from meat products. Brain and SC tissues were added to grind meats in different concentrations and respective absorption values were obtained using Ridascreen^® test kit. The kit detected both brain and SC at 0.1%, below its claimed sensitivity level, for brain and SC combined. Thus, using this commercial test kit, we tested cross-section of samples sold in Obihiro area, Japan. In the test standard controls 0, 0.2%, 1% and 2% were practiced. All most all the tested samples absorption values near to standard 0, and it is concluded that all the samples that we tested were absence or at a very minimal levels of SRM.     

Carbon recycle nuclear hydrogen carrier system for transportation field

Possibility of a carbon recycle hydrogen carrier system driven by nuclear power for transportation field was discussed. The hydrogen carrier system, which was zero carbon dioxide emission and small hydrogen compression work and explosion risk, was examined for fuel cell vehicles. The combination of the hydrogen carrier system with a high-temperature gas reactor was proposed. It was expected that the carrier system realized lower pressure and safe storage of hydrogen consisting with the similar energy efficiency of conventional water electrolysis hydrogen system. Carbon neutral bio-mass energy system and the carrier system were compared for the next generation vehicle energy system. Bio-mass energy had the limitation of quantity and would take small part of vehicle market in Japan. Nuclear assisted bio-mass hydrogen system could enhance yield of bio-fuels under carbon neutral. The carbon recycle nuclear hydrogen carrier system was expected to be applicable to the demand of much more larger number of vehicles because it was free from the limitation of bio-mass carbon quantity.     

Prediction of coiling conditions of plate in coilbox by controlled FEM simulation

A method using the finite element simulation for predicting coiling conditions of intermediate plates in a coilbox installed between roughing and finishing stands of hot strip rolling is proposed. In the coilbox, the intermediate plate is coiled to prevent the drop in temperature due to the radiation from the surface of the plate in the waiting period. In the present method, non-steady-state deformation of the plate in the coilbox is simulated by the finite element method, and the rolls are appropriately moved in accordance with the simulated results to form the plate in a coil. Since the formation of the coil is influenced by the bending shape near the front end of the plate, the deformation behaviour near the front end is monitored in the finite element simulation, and the positions of the rolls for coiling the plate are determined from instantaneous movement of the rolls once without trial and error. In addition, the coiling is stabilised by controlling the rotation of the roll. The predicted coiling conditions are applicable to actual coilbox machines.     

Solubilities of NiO and LaNiO3 in Li/Na eutectic carbonate with rare-earth oxide

For the commercial application of molten carbonate fuel cells (MCFCs) under high-pressure operation, the problem of Ni shorting should be solved that is closely related to the solubility of cathode material. In order to improve the MCFC cathode stability, effects of the addition of rare-earth metal oxides to the molten carbonates have been quantitatively investigated. Especially, La₂O₃ addition to the molten carbonate significantly decreased the solubility of NiO. Such low solubility of NiO was caused by effects of both the acid-base equilibrium of molten carbonate and the activity of Ni in solid by the formation of complex oxide. Solubilities of LaNiO₃ and Nd₂NiO₄ were also smaller than that of NiO in molten carbonate as the same reason as that of NiO in the molten carbonates with saturated La₂O₃. Based on the data of solubility, a new parameter was proposed to evaluate the solubility of metal ion in molten carbonates. This parameter concerned with the acid-base equilibrium of melts and the activity of solid for the metal oxide. A linear relationship with the measured solubility of metal oxide in molten carbonates was obtained by this parameter. It would be indicated that the parameter is useful for the prediction of metal oxide solubilities in molten carbonates.     

Luminescent Properties of Sintered Spherical Silica With Alkali Metal Oxide Additives

The correlation of luminescent properties to the polymorphism in sintered amorphous spherical silica with alkali metal additives has been investigated. The luminescent properties and the crystalline phases changed with the different kinds of alkali metal additives, and the firing temperature. The blue luminescence at 470 nm was observed for all amorphous sintered silica containing Na₂O, K₂O, Rb₂O or Cs₂O, while the yellowish green luminscence at 545 nm was for some crystalline sintered silica. The blue luminescence was assumed to be related to defects produced by dehydration of silanol groups and the yellowish green ones in crystalline and liquid phases.     

Copper as a Collaborative Partner of Zinc-Induced Neurotoxicity in the Pathogenesis of Vascular Dementia

Copper is an essential trace element and possesses critical roles in various brain functions. A considerable amount of copper accumulates in the synapse and is secreted in neuronal firings in a manner similar to zinc. Synaptic copper and zinc modulate neuronal transmission and contribute to information processing. It has been established that excess zinc secreted during transient global ischemia plays central roles in ischemia-induced neuronal death and the pathogenesis of vascular dementia. We found that a low concentration of copper exacerbates zinc-induced neurotoxicity, and we have demonstrated the involvement of the endoplasmic reticulum (ER) stress pathway, the stress-activated protein kinases/c-Jun amino-terminal kinases (SAPK/JNK) signaling pathway, and copper-induced reactive oxygen species (ROS) production. On the basis of our results and other studies, we discuss the collaborative roles of copper in zinc-induced neurotoxicity in the synapse and the contribution of copper to the pathogenesis of vascular dementia.