博物馆藏品的除藏与归还

博物馆处于一种变动不居的状态,正逐步偏离其原来所构想的发展方向——致力于永久收藏和保存有价值的物品和标本。但是,现在这一长期持有藏品的发展方向正受到根源于博物馆内外因素的挑战,促使博物馆另辟蹊径,根据其与所服务社区之间的变动关系来管理藏品。特别是,土著民族要求归还其文化物品(这些物品通常是在可疑的情况下被盗用的)的请求越来越多,迫使博物馆重新调整自己的思路,准备适当的政策,并付诸实施。随着藏品归还成为名副其实的藏品除藏过程,博物馆日益置身于道德和伦理的领导位置,纠正过去所犯下的错误,促进合作,为社会的公平、和谐作出努力。

Adaptive foreground and shadow segmentation using hidden conditional random fields

Video object segmentation is important for video surveillance, object tracking, video object recognition and video editing. An adaptive video segmentation algorithm based on hidden conditional random fields (HCRFs) is proposed, which models spatio-temporal constraints of video sequence. In order to improve the segmentation quality, the weights of spatio-temporal con- straints are adaptively updated by on-line learning for HCRFs. Shadows are the factors affecting segmentation quality. To separate foreground objects from the shadows they cast, linear transform for Gaussian distribution of the background is adopted to model the shadow. The experimental results demonstrated that the error ratio of our algorithm is reduced by 23% and 19% respectively, compared with the Gaussian mixture model (GMM) and spatio-temporal Markov random fields (MRFs).

Cooperative Interference Game in Cognitive Radio Hidden Terminal Scenario

Hidden terminal problem in spectrum sensing is one of the most challenging problems in cognitive radio network(CRN).To tackle this problem,we propose a novel Cooperative Interference Game scheme in this paper.The scheme adopted full duplex(FD)mode to sense over multiple sub-bands in an iterative manner without extra sensing devices.The implementation algorithm of the proposed scheme is consisted of three modules:the formulation of the maximum transmit power limitation of second user(SU);the self-interference cancellation coefficient;and the optimal location of SU for an optimized low collision probability.Monte Carlo simulation proved that compared with cooperative spectrum sensing,the proposed scheme significantly improves the performance of spectrum detection and mitigates hidden terminal problem to a large extent with less energy consumption.

Distribution patterns of benthic diatoms during summer in the Niyang River,Tibet,China

The aim of this study was to investigate the distribution, density, community structure and biodiversity characteristics of benthic diatoms, and to analyze whether differences in species composition and abundance exist in different regions of the Niyang River, Tibet. Among the 157 taxa observed in 15 sampling sites in the main river and tributary, most were casual species （〉100）, the relative abundance of the genera Achnantkes and Fragilaria was 67% of the total relative abundance. Acknantkes minutissima was the most important species and dominated the whole river reaches （average relative abundance was 30%）; the average diatom densities were 7.4 x 105 cell/cm2 at all sites, and increased slowly from the upper section to downriver. The significant indicator taxa with higher relative abundance were Achnanthes biasolettiana （18.0%） and Fragilaria arcus （18.2%）, Fragilaria capucina var. vaucheriae （31.2%）, Fragilaria construens var. renter （11.3%） and Cymbella affinis （11.0%） in the upper, tributary and mid-river sections, respectively. Achnanthes minutissima was the most abundant species （56%） in the downriver section. Biodiversity indices showed a gradual decrease from the up- to down-river section, and dominant species were more abundant in the upper and mid-river sections than in the downriver section. A two-way indictor species analysis （TWINSPAN） of diatom composition clearly showed four different groups, namely the upper, mid, lower and tributary sections. Detrended correspondence analysis （DCA） supported the results of TW1NSPAN, and the characteristics of site distribution and species composition in the Niyang River supported the spatial structure of diatom assemblages. This study indicates that bio-assessment programs utilizing benthic diatoms could clearly benefit lotic water with regional stratification.

Species Richness and Diversity of Alpine Grasslands on the Northern Tibetan Plateau:Effects of Grazing Exclusion and Growing Season Precipitation

Species richness and diversity indices （Shannon-Wiener index, Simpson dominance index and Pielou evenness index） in alpine grassland ecosystems （alpine meadow, alpine steppe and desert steppe） under grazing-excluded and freely grazed sites were investigated along the Northern Tibetan Plateau Alpine Grassland Transect during summer 2009 and 2010. We found that species richness and diversity have not been significantly altered by short-term grazing exclusion since 2006 at vegetation and regional scales. Species richness and diversity were mainly driven by growing season precipitation （GSP）, which accounted for over 87 % of the total variation observed, Species richness and diversity at grazing- excluded and freely grazed sites appear to respond to growing season precipitation in parallel. Species richness exponentially increased with GSP while diversity indices showed positively linear relationships with GSP. This indicates that GSP on the Northern Tibetan Plateau is crucial in regulating species richness and diversity and should be taken into account in future studies on alpine grassland conservation.