Enhanced Efficiency of Metamorphic Triple Junction Solar Cells for Space Applications

Metamorphic In0.55Ga0.45P/In0.06Ga0.94As/Ge triple-junction （3J-MM） solar cells are grown on Ge （100） sub- strates via metal organic chemical vapor deposition. Epi-structural analyses such as high resolution x-ray diffrac- tion, photoluminence, cathodoluminescence and HRTEM are employed and the results show that the high crystal quality of 3J-MM solar cells is obtained with low threading dislocation density of graded buffer （an average value of 6.8× 10^4/cm2）. Benefitting from the optimized bandgap combination, under one sun, AM0 spectrum, 25℃ conditions, the conversion efficiency is achieved about 32%, 5% higher compared with the lattice-matched In0.49Ga0.51P/In0.01Ga0.99As/Ge triple junction （3J-LM） solar cell. Under 1-MeV electron irradiation test, the degradation of the EQE and I-V characteristics of 3J-MM solar cells is at the same level as the 33-LM solar cell. The end-of-life efficiency is -27.1%. Therefore, the metamorphic triple-junction solar cell may be a promising candidate for next-generation space multi-junction solar cells.

Space- and time-efficient approach for virtual machine provisioning

As a new promising paradigm, cloud computing can make good use of economics of scale and elastically deliver almost any IT related services on demand. Nevertheless, one of the key problems remaining in cloud computing is related to virtual machine images, which require a great amount of space/time to reposit/provision, especially with diverse requests from thousands of users simultaneously. In this paper, by using the splitting and eliminating redundant data techniques, a space and time efficient approach for virtual machines is proposed. The experiments demonstrate that, compared with existing solutions, our approach can conserve more disk space and speed up the provisioning of virtual machines.

A Comparative Study on Two Techniques of Reducing the Dimension of Text Feature Space

With the development of large scale text processing, the dimension of text feature space has become larger and larger, which has added a lot of difficulties to natural language processing. How to reduce the dimension has become a practical problem in the field. Here we present two clustering methods, i.e. concept association and concept abstract, to achieve the goal. The first refers to the keyword clustering based on the co occurrence of

Eco-sustainability Assessment of Building Projects Based on Eco-footprint

The life-cycle eco-footprint computing model of building projects was established in the study. It contained the eco-footprint in 4 aspects during the lifecycle: consumed energy, consumed resource, emitted carbon dioxide and produced solid waste. Space efficiency of life-cycle eco-footprint index was proposed and used to assess the eco-sustainability of building projects. Then, the eco-footprint and ecosustainability of 4 different structure types(brick-concrete bungalow, multi-storey brick-concrete, multistorey steel-concrete, high-rise steel-concrete) for residential building in severely cold areas were investigated. The results indicated that: 1) Compared with bungalow, high-rise building with relatively smaller shape coefficient and window-wall ratio had higher eco-sustainability; 2) For the buildings with the same storey, shape coefficient and window-wall ratio, steel-concrete building had higher eco-sustainability than brickconcrete building; 3) High-rise steel-concrete structure had the greatest eco-sustainability during the 4 different bui lding structures, so it was more suitable to promote.

Experimental and simulation optimization analysis of the Whipple shields against shaped charge

Occasionally, the Whipple shields are used for the protection of a space station and a satellite against the meteoroids and orbital debris. In the Whipple shields each layer of the shield depletes part of high speed projectile en- ergy either by breaking the projectile or absorbing its energy. Similarly, this investigation uses the Whipple shields against the shaped charge to protect the light armour such as infantry fighting vehicles with a little modification in their design. The unsteady multiple interactions of shaped charge jet with the Whipple shield package against the steady homogeneous target is scrutinized to optimize the shield thickness. Sim- ulations indicate that the shield thickness of 0.75 mm offers an optimum configuration against the shaped charge. Exper- iments also support this evidence.

Analysing the effect of stand density and site conditions on structure and growth of oak species using Nelder trials along an environmental gradient:experimental design,evaluation methods,and results

Background: Most current approaches in forest science and practice require information about structure and growth of individual trees rather than- or in addition to- sum and mean values of growth and yield at forest stand level as provided by classic experimental designs. By inventing the wheel design, Nelder provided the possibility to turn to the individual tree as basic information unit. Such trials provide valuable insights into the dependency of growth on stand density at particular sites.Methods: Here, we present an extension of the original design and evaluation by Nelder.(i) We established Nelder wheels along an environmental gradient through Europe in atlantic climate in Belgium and Germany, Mediterranean climate in Italy, continental climate in Hungary as well as on high land climate in Mexico. Such disjunct Nelder wheels along an environmental gradient can be regarded and analysed as a two-factor design with the factors of site condition and stand density.(ii) We present an advanced statistical approach to evaluate density dependent growth dynamics of trees planted in form of the Nelder design, which considers spatio-temporal autocorrelation.(iii)We prove the usefulness of the methods in improving ecological theory concerning density related productivity,trade-offs between facilitation and competition, and allometric relations between size variables.Results: First evaluations based on remeasured Nelder wheels in oak(Quercus robur L.) show a size growth differentiation during the first observation period. In particular, height growth is accelerated under higher competition indicating facilitation effects. We detect furthermore a high variability in allometric relations.Conclusions: The proposed design, methods, and results are discussed regarding their impact on forest practice,model building, and ecological theory. We conclude that the extended Nelder approach is highly efficient in providing currently lacking individual tree level information.

MemSC： A Scan-Resistant and Compact Cache Replacement Framework for Memory-Based Key-Value Cache Systems

Memory-based key-value cache systems, such as Memcached and Redis, have become indispensable components of data center infrastructures and have been used to cache performance-critical data to avoid expensive back-end database accesses. As the memory is usually not large enough to hold all the items, cache replacement must be performed to evict some cached items to make room for the newly coming items when there is no free space. Many real-world workloads target small items and have frequent bursts of scans （a scan is a sequence of one-time access requests）. The commonly used LRU policy does not work well under such workloads since LRU needs a large amount of metadata and tends to discard hot items with scans. Small decreases in hit ratio can result in large end-to-end losses in these systems. This paper presents MemSC, which is a scan-resistant and compact cache replacement framework for Memcached. MemSC assigns a multi-granularity reference flag for each item, which requires only a few bits （two bits are enough for general use） per item to support scanresistant cache replacement policies. To evaluate MemSC, we implement three representative cache replacement policies （MemSC-HM, MemSC-LH, and MemSC-LF） on MemSC and test them using various workloads. The experimental results show that MemSC outperforms prior techniques. Compared with the optimized LRU policy in Memcached, MemSC-LH reduces the cache miss ratio and the memory usage of the resulting system by up to 23% and 14% respectively.