Damage to and recovery of coastlines polluted with C-heavy oil spilled from the Nakhodka

The damage to and recovery of the Japanese coastline from Suzu, Ishikawa Prefecture to Mikuni, Fukui Prefecture was investigated visually over three years after a C-heavy oil spill from the Russian tanker "Nakhodka" in the Japan Sea on January 2, 1997. The beached C-heavy oil tended to remain for a long time on coasts of bedrock and boulder/cobble/pebble but it was removed rapidly from coasts of gravel/sand and man-made structures such as concrete tetrapods. On the coasts of the latter type, wave energy appeared to be the main force removing the oil. One year after the spill, C-heavy oil tended to remain strongly on the sheltered coasts of bedrock and boulder/cobble/pebble. Even on coasts of this type, the contamination was remarkably absent by 2 years after the spill. The concentration levels of polycyclic aromatic hydrocarbons (PAHs) in oil lumps, sand and seawater were monitored during 3 years following the spill. The concentrations of PAHs having 2 or 3 rings decreased more quickly than did those of PAHs having 4 or more rings, suggesting that volatilization was the main cause of the decrease. On the other hand, the concentrations of PAHs having 4 to 6 rings did not start to decrease until 7 months after the spill. The main cause of the decrease seemed to be photolysis. The concentration of BaP in seawater off the polluted coasts was high 1 month after the spill and then decreased. Three years after the spill, the level fell to the sub ng/L level, which was as low as the level in seawater along unpolluted clean coasts in Japan. The concentration of BaP in greenling was higher than the normal level only during the first two months after the spill. These results suggest that the coastlines in Ishikawa and Fukui Prefectures that were polluted with C-heavy oil recovered in 3 years.     

Accumulation of uranium derived from long-term fertilizer applications in a cultivated Andisol

The U concentrations in the soils of experimental fields with continuous fertilizer applications and in neighboring non-agricultural soils were determined. The surface soils in the three experimental fields with fertilizer applications contained higher amounts of U compared with the non-agricultural surface soils. The amount of U elevated in the soil was estimated by the vertical profile of U concentration, and an increase of about 200 mg m-2 of U was found in the soils at 0-35 cm depth during a 61-year cultivation period. The estimated value was almost the same as the amount of U added through the fertilizers as calculated from U concentrations in the applied fertilizers. Therefore, almost all the U from the fertilizers would still remain in the upper part of the soils. Chemical extraction results suggested that organic substances and noncrystalline clay minerals in the surface soil should play an important role for accumulation of U derived from the fertilizers.     

A new method for evaluating biological safety of environmental water with algae, daphnia and fish toxicity ranks

In this study, an innovative approach to evaluate biological safety of environmental water with toxicity ranks was proposed. Widely used species, algae (Selenustrum capricornutum), daphnia (Daphnia magna) and fish (Oryzias latipes larvae) belonging to three trophic levels in aquatic ecosystem, were selected and combined as a test set to measure the bio-toxicity of water sample. Maximum exposure concentrations for algae, daphnia and fish test were respectively designed as 10-, 50- and 50-fold of river water based on a simplification of conventional toxicity extrapolation method EU Directive EEC/93/67. A novel assessment index "safety score" of 1, 2, 3 and 4 with 1 being the safest was established for normalizing the toxicity effects. Safety score was determined according to the highest exposure concentration where adverse ecotoxicological effects could not be observed, and a triangle figure was designed to visually describe the safety scores of three toxicity tests. Finally, in order to conveniently evaluate the biological safety of environmental water, an integrated assessment index "bio-safety rank" (BSR) was established and determined according to the safety scores of the three tests, and with the index BSR, water sample could be ranked as A, B, C or D with A being the safest. It was shown that the proposed new method was effective for screening and evaluating the biological safety of river water in case studies.     

Manganese doped gallium oxynitride prepared by nitridation of citrate precursor

Manganese doping of gallium oxynitride was investigated to obtain a magnetic semiconductor by nitriding a precursor in ammonia flow. The precursor was obtained by prefiring a mixed gel made of Mn²⁺ and Ga³⁺ nitrates and citric acid in aqueous solution. The products were isostructural with hexagonal GaN. The doping limit was 10 and 5 at% in the samples nitrided at 750 and 850 °C, respectively. Chemical analysis of the products suggested that they were manganese doped gallium oxynitrides. Oxide and nitride ions were randomly distributed in the anion sites in the latter product. Manganese oxide cluster might be formed in the former. The product nitrided at 850 °C showed an antiferromagnetic interaction with a Weiss temperature θ = −38 K, while the product nitrided at 750 °C was paramagnetic.     

Collection efficiency of cylindrical and elliptic cyclone dust collectors with vortex breaker

IntroductionUntil now there are many papers concerning thecollection efficiency and the cut-size Xo for thereturned type, axial type and also rotary flow typesof the cyclone dust collectors[1'2'3'4]. The crosssection of these cyclones is the circular cylindricalbody. One of the main reasons for the circularsection is that the flow control on the threedimensional turbulent rotational flow becomeseasy and also the movement of the solid particlesalong the concave wall surface becomes smooth. Sot…     

Influence of morphology on photo‐degradation of low density polyethylene films

The effect of the morphology on photo‐degradation was investigated for low‐density polyethylene materials. For this purpose, films with different degrees of crystallinity and different degrees of orientation were prepared. For all the films, photodegradation was promoted at 336K for 12 days using a weather meter. The following results were obtained. There existed an induction period before degradation or chain scission. The induction period was longer for stretched films than for un‐stretched ones. Also, the rate of degradation became lower for stretched films. However, both the induction period and the rate of degradation hardly changed with heat‐treatment condition, that is, the degree of crystallinity. In the induction period, the density changed in a complicated manner. This complicated change must be due to the change in the molecular aggregation state of the amorphous phase. The rheological and GPC measurements indicated that photo‐degradation causes the lowering of molecular weight and the increase in higher molecular weight fraction, and consequently the broadening of molecular weight distribution. The lowering of molecular weight may be caused by chain scission and the increase in higher molecular weight fraction by the formation of crosslinks.     

Analysis and study of a handoff scheme with multiple priority strategies

A handoff scheme with the combination of channel reservation and preemptive priority in integrated voice/data cellular mobile systems is proposed. In the scheme, calls are divided into three different classes: handoff voice calls, originating voice calls, and data calls. An access strategy with the combination of channel reservation and preemptive priority is provided to a handoff voice call. Furthermore, in order to improve the system capacity for the total voice traffic, preemptive priority is also given to partial originating voice calls. The system is modeled by a two-dimensional Markov chain. Both the iteration method and the approximate method are used to calculate and analyze some of the most important performance measures of the system. It is shown that our scheme can provide better quality of services for mobile subscribers.     

制备工艺对热压烧结SiC/SiC复合材料结构与性能的影响

采用纳米SiC和亚微米SiC粉料作为基体形成原料,通过热压烧结技术制备了SiC/SiC 复合材料.研究了粉料颗粒、烧结温度、烧结压力对复合材料显微结构和各种性能的影响.结果显示,采用纳米碳化硅粉体可有效降低烧结温度,促进复合材料的致密化过程,在1780℃、20MPa条件下可获得性能优良的复合材料.而采用亚微米SiC粉体,复合材料的致密化过程需要较高的温度,但随着密度的增加,基体与纤维之间的作用力增强,不利于性能的提高.     

The adsorption and activation properties of precious metal clusters toward NO: a density functional study

Adsorption and activation properties of precious metal clusters such as Ir, Pt, and Au toward NO were investigated by means of the density functional calculations. We focused on the geometrical features of model clusters such as the shape and the number of consisting atoms that could determine the ability for the adsorption and the activation of NO. We found that the order of the energetical stability of the adsorption states of NO can be described as Ir > Pt > Au. It depends on neither the shape of the pentaatomic clusters nor the number of atoms in the model clusters considered. The ability of the precious metal clusters for the activation of the N–O bond were also discussed from both vibrational and geometrical points of view. The substantial activation of the N–O bond was found on both the NO/Ir₅ and the NO/Pt₄ systems, indicating that the specific adsorption geometries enhance the ability for the activation of the N–O bond. These results indicate that the Ir cluster has the best properties for the adsorption and activation of NO. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ballistic electron emission from quantum-sized nanosilicon diode and its applications

A quantum confinement effect renders silicon a functional wide-gap material with useful functions. For instance, a diode based on nanocrystalline silicon (nc-Si) exhibits characteristic quasi-ballistic emission effects in various media. As means for physical excitation and probing, the applicability to parallel electron beam lithography and high-sensitivity image-pickup has been demonstrated in vacuum. The energetic electron incidence into air and Xe ambient induces negative ion generation by electron attachment into oxygen molecules and vacuum ultraviolet light emission by internal excitation of Xe molecules, respectively. Another effect is that the nc-Si ballistic emitter can supply highly reducing electrons into aqueous and metal-salt solutions without the use of counter electrodes. This is an attractive process that will be applicable to hydrogen generation and thin metal film deposition.