A sustainable PWR fuel cycle with complete TRU recycling using fertile-free fuel

The feasibility of a conventional PWR fuel cycle with complete recycling of TRU elements in the same reactor is investigated. A new Combined Non-fertile and Uranium (CONFU) fuel assembly where about 20% of the uranium fuel pins are replaced with fertile free fuel (FFF) hosting TRU generated in the previous cycle is proposed. In this sustainable fuel cycle based on the CONFU fuel assembly concept, the amount and radiotoxicity of the nuclear waste can be significantly reduced in comparison with the conventional once-through UO 2 fuel cycle. It is shown that under the constraints of acceptable power peaking limits, the CONFU assembly exhibits negative reactivity feedback coefficients comparable in values to those of the reference UO2 fuel. Moreover, the effective delayed neutron fraction is about the same as for UO2-fueled cores. Therefore, feasibility of the PWR core operation and control with complete TRU recycle has been shown in principle. However, gradual build up of small amounts of Cm and Cf challenges fuel reprocessing and fabrication due to the high spontaneous fissions rates of these nuclides and heat generation by some Pu, Am, and Cm isotopes. Feasibility of the processing steps becomes more attainable if the time between discharge and reprocessing is 20 years or longer. The implications for the entire fuel cycle will have to be addressed in future studies.

西藏硅藻的新种类(Ⅱ)

<正> 本文仅将在西藏发现的硅藻门,舟形藻属Navicula中的2新变种、曲壳藻属Achnanthes中的2新种作一报道,附图均按西藏标本绘制。1 布鲁克曼舟形藻波缘变种 新变种 图1:1

Spatial distribution of benthic algae in the Gangqu River, Shangrila, China

This study consisted of sampling benthic algae at 32 sites in the Gangqu River, an important upstream tributary of the Yangtze River. Our aims were to characterize the benthic algae communities and relationships with environmental variables. Among the 162 taxa observed, Achnanthes linearis and Achnanthes lanceolata var. elliptica were the dominant species (17.10% and 14.30% of the total relative abundance, respectively). Major gradients and principal patterns of variation within the environmental variables were detected by principal component analysis (PCA). Then non-metric multidimensional scaling (NMS) divided all the sites into three groups, which were validated by multi-response permutation procedures (MRPP). Canonical correspondence analysis (CCA) indicated that three environmental variables (TN, TDS, and TP) significantly affected the distribution of benthic algae. Weighted averaging regression and cross-calibration produced strong models for predicting TN and TDS concentration, which enabled selection of algae taxa as potentially sensitive indicators of certain TN and TDS levels: for TN, Achnanthes lanceolata, Achnanthes lanceolata var. elliptica, and Cymbella ventricosa var. semicircularis; for TDS, Cocconeis placentula, Cymbella alpina var. minuta, and Fragilaria virescens. The present study represents an early step in establishing baseline conditions. Further monitoring is suggested to gain a better understanding of this region.

Benthic algae of the Gangqu River, Shangrila, China

We surveyed the benthic algae at 32 sites in the Gangqu River system during May 2005. Among the 162 different taxa observed, 88.8% were diatoms. Achnanthes linearis and Achnanthes lanceolata var. elliptica were the dominant species, comprising 17.1% and 14.3% of the total relative abundance, respectively.

Evidence of host specificity and congruence between phylogenies of bitterling and freshwater mussels

Evidence of host specificity and congruence between phylogenies of bitterling and freshwater mussels. Zoological Studies 45(3): 428-434. Bitterling (Cyprinidae: Acheilognathinae) are freshwater fishes with a unique spawning relationship with freshwater mussels on whose gills they lay their eggs. During the breeding season of bitterling fishes, we collected 843 mussels belonging to 16 species from Lake Qinglan, central China and examined their gill chambers for the presence of bitterling larvae. Three species of bitterling larvae were identified; Acheilognathus tonkinensis, Ach. cf. meridianus, and Ach. barbatulus, in 3 species of mussel: Unio douglasiae, Lamprotula caveata, and L. tortuosa, suggesting host specialization. Using our own and other published data, we compared the respective phylogenies of bitterling and mussels, but failed to show clear congruence. However, broad specializations are evident, with Acheilognathus and Tanakia showing preferences for mussels with a relatively simple gill structure (Ableminae), and Rhodeus spp. showing preferences for mussels of the Anodontinae and Unioninae, which have more-complex gill structures.

Effects of age and dietary protein level on digestive enzyme activity and gene expression of Pelteobagrus fulvidraco larvae

The present research studied the effects of age and dietary protein level on pepsin, trypsin and amylase activity and their mRNA level in Petteobagrus fulvidraco larvae from 3 to 26 days after hatch (DAH). Three DAH larvae were fed three isoenergetic diets, containing 42.8% (CP 43), 47.3% (CP 47) and 52.8% (CP 53) crude protein. Live food (newly hatched Artemia, unenriched) was included as a control. The effects of age on enzyme activity and mRNA were as follows: pepsin and trypsin activity in all treatment groups showed a significant (P < 0.05) increase at the beginning and decrease later although the timing of decrease was not the same among treatment groups and between the digestive enzymes. Pepsin and trypsin mRNA level followed the pattern of their respective enzyme changes. Age significantly affected amylase activity (P < 0.05) while age had no effect on amylase mRNA during the experimental period. The four diets significantly (P < 0.05) affected activity and mRNA level of pepsin and trypsin. Diets did not affect amylase activity or mRNA level. These results suggest that the effects of age on pepsin and trypsin gene expressions are at the transcriptional level. Dietary protein level does affect pepsin and trypsin gene expression in the early life of P. fulvidraco. There were no transcriptional effects on amylase gene expression. (c) 2005 Elsevier B.V. All rights reserved.

Variation of benthic diatoms in a shallow, eutrophic Chinese Lake, Lake Donghu

Benthic diatom communities were sampled monthly from May 2004 to May 2005 at four different sites in the littoral zone of Lake Donghu, a shallow eutrophic lake of China. The seasonal patterns of the total abundance, which were lowest in summer and highest in spring, were found at all sites. Total densities of diatom assemblages were significantly higher at hyper-eutrophic sites than at moderately eutrophic sites. Melosira varians was the most abundant species and dominant contributor to total abundance at all sites during spring, autumn and winter, whereas Achnanthes exigua dominated benthic diatom assemblages at the site with the highest nutrient concentrations during the summer. Achnanthes lanceolata var. dubia, Gomphonema parvulum, Navicula similis, Navicula verecunda and Nitzschia amphibia were generally observed at all sites throughout the year and were dominant at higher-nutrient sites. The abundance of ambient nutrients was probably responsible for the spatial variation in biomass, composition and diversity of benthic diatom assemblages, and lake water temperature was the major factor that controlled seasonal distribution.

Benthic algae of the Xiangxi River, China

From June 2000 to June 2002, four sites on the mainstem of the Xiangxi River and one site on each of its major tributaries were sampled 16 times each for benthic algae. All total, 223 taxa (most to species and variety levels) were found (193 Bacillariophyta, 20 Chlorophyta, nine Cyanophyta and one Xanthophyta). The diatoms Cocconeis placentula, Achnanthes linearis, and Diatoma vulgare dominated the system, with relative abundance of 33.3%, 18.8%, and 6.4%, respectively. The abundances of all the other taxa were under 5%, and 210 taxa collectively contributed less than 1% of the total abundance. Taxa diversity peaked in winter and reached a minimum in summer. Species richness varied considerably but was not significantly different over time. Maximum algal density occurred in later winter/spring (1.4 x 10(9) ind./m(2)) but was not significantly different from the minimum density, which occurred in August. Chlorophyll a showed similar seasonal fluctuation but also was not significantly different over time. Canonical correspondence analysis demonstrated that water hardness, depth, conductivity, and alkalinity had important influences on variation of epilithic algae in the Xiangxi River system.

Moisture content in Dall's porpoise (Phocoenoides dalli) tissues: a reference base for conversion factors between dry and wet weight trace element concentrations in cetaceans

Concentration of trace elements measured by dry weight basis has become more commonly used in recent studies on cetaceans than wet weight basis, which was used more in earlier studies. Because few authors present moisture content data in their papers, it is difficult to compare the concentrations of trace elements between various studies. Therefore, we felt that it would be useful if a reference conversion factor (CF) for tissue types could be found to convert between wet weight and dry weight data on trace element concentrations. We determined the moisture contents of 14 tissues of Dall's porpoise (Phocoenoides dalli), and then, calculated the CF values for those tissues. Because the moisture content of each tissue differs from other tissues, it is necessary to use a specific CIF for each tissue rather than a general CF for several tissues. We have also found that CIF values for Dall's porpoise tissues are similar to the same tissues in other cetaceans. Therefore CF values from Dall's porpoise can be reliably used to convert between wet and dry weight concentrations for other cetacean tissues as reference data. (C) 2002 Elsevier Science Ltd. All rights reserved.

Effect of feeding strategy and carbohydrate source on carbohydrate utilization by white sturgeon (Acipenser transmontanus) and hybrid tilapia (Oreochromis niloticus X O-aureus)

Two 8-week growth trials were conducted to determine the effect of continuous (CF) versus 2 meals day(-1) (MF) feeding and 30% starch versus 30% glucose diets on the carbohydrate utilization of 9.0-g white sturgeon and 0.56-g hybrid tilapia. The two trials were conducted under similar conditions except that sturgeon were kept at 18.5 degrees C in a flow-through system and tilapia were kept at 26 degrees C in a recirculating system. Significantly (P less than or equal to 0.05) higher specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), body lipid content and liver glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activities were observed in the CF than MF sturgeon. Only SGR, FE and PER were higher in sturgeon fed the starch than the glucose diets. Only higher liver G6PDH and malic enzyme (ME) activities were observed in the CF than MF tilapia but higher SGR, FE, PER and liver G6PDH, 6PGDH and ME activities were observed in tilapia fed the starch diet than those fed the glucose diet. This suggested that carbohydrate utilization by sturgeon was more affected by feeding strategy whereas tilapia was more affected by carbohydrate source. Furthermore, white sturgeon can utilize carbohydrates better than hybrid tilapia regardless of feeding strategy and carbohydrate source.

量子点中强关联电子的输运性质

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

Direct observation of excitonic polaron in InAs/GaAs quantum dots

We report a direct observation of excitonic polaron in InAs/GaAs quantum dots using the photoluminescence (PL) spectroscopy. We observe that a new peak s' emerges below the s-shell which has anomalous temperature dependence emission energy. The peak s' anticrosses with s at a certain temperature, with a large anticrossing gap up to 31 meV. The behavior of the new peak, which cannot be interpreted using Huang-Rhys model, provides a direct evidence for strong coupling between exciton and LO phonons, and the formation of the excitonic polaron. The strong coupling between exciton and phonons opens a way to coherently control the polaron states.

NIP a-Si : H solar cells on stanless steel with p-type nc-Si : H window layer

The successful application of boron-doped hydrogenated nanocrystalline silicon as window layer in a-Si: H nip solar cells on stainless steel foil with a thickness of 0.05 mm is reported. Open circuit voltage and fill factor of the fabricated solar cell were 0.90V and 0.70 respectively. The optical and structural properties of the p-layers have been investigated by using UV-VIS and Raman spectroscopy. It is confirmed that the p-layer is hydrogenated nanocrystalline silicon with a wide optical gap due to quantum size effect.

AMPS modeling of light J-V characteristics of a-Si based solar cells

AMPS (Analysis of microelectronic and photonic structures) mode,which was developed by Pennsylvania State University, has been used to module the light J-V characteristics of a-Si solar cells with a structure of TCO/p-a-SiC:H/i-a-Si:H/n-a-Si:H/ metal. The effects of valence band offset and contact barriers at p/i and TOC/p, n/metal interfaces on the light J-V characteristics have been examined. The modeling has qualitatively categorized and explained the non-ideal J-V behaviors (rollover, crossover, Voc shift,and rollunder) observed in a-Si based solar cells.

Hydrogen passivation of multi-crystalline silicon solar cells

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper. Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.