Fixed collision rate back-off scheme for collision resolution in wireless networks

This investigation proposes a fixed collision rate (FCR) back-off algorithm for wireless networks. The proposed scheme takes advantage of the central unit (CU) in a wireless network to broadcast a common back-off window size to all the users, significantly alleviating the unfairness of bandwidth utilization in conventional binary exponential back-off (BEB) algorithms. It is shown that, when maximum throughput is achieved, collision rate is almost a constant for any traffic load. In the operation of the FCR, the CU dynamically adjusts the back-off window size to keep the collision rate at a constant level for maximum throughput. Simulation results demonstrate that the unfairness of bandwidth utilization in the BEB is significantly lessened and the throughput can be maintained at e^-1≈0.368 when the number of users approaches infinity. The capture effect even further improves system performance.     

Identification of gaps in mangrove forests with airborne LIDAR

Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for investigating this issue. Airborne light detection and ranging (LIDAR) technology provides an effective way for identifying gaps by remotely obtaining direct measurements of ground and canopy elevations. A method based on an alternative sequential filter and black top-hat mathematical morphological transformation was developed to extract gap features. Comparison of identified gap polygons with raw LIDAR measurements and field surveys shows that the proposed method successfully extracted gap features in mangrove forests in Everglades National Park. There are 400–500 lightning gaps per square kilometer in mangrove forests at the study sites. The distribution of gap sizes follows an exponential form and the area of gaps with sizes larger than 100 m² account for 55–61% of the total area of gaps. The area of gaps in the mangrove forest in Everglades National Park is about 4–5% of the total forest area and the average gap formation rate is about 0.3% of the total forest area per year, indicating that lightning gaps play an important role in mangrove forest dynamics.     

Detrended Fluctuation Analysis of the Human EEG during Listening to Emotional Music

A nonlinear method named detrended fluctuation analysis （DFA） was utilized to investigate the scaling behavior of the human electroencephalogram （EEG） in three emotional music conditions （fear, happiness, sadness） and a rest condition （eyes-closed）. The results showed that the EEG exhibited scaling behavior in two regions with two scaling exponents β1 and β2 which represented the complexity of higher and lower frequency activity besides α band respectively. As the emotional intensity decreased the value of β1 increased and the value of β2 decreased. The change of β1 was weakly correlated with the ＇approach-withdrawal＇ model of emotion and both of fear and sad music made certain differences compared with the eyes-closed rest condition. The study shows that music is a powerful elicitor of emotion and that using nonlinear method can potentially contribute to the investigation of emotion.     

坨五站中间乳化层快速增长原因及治理方案

胜利采油厂坨五站高含水(95％)原油化学预脱水中，二级沉降罐内油水相之间的中间乳化层增长迅速，引起了一系列问题。现场调查和大量室内测试结果表明，产生这一现象的原因有：油溶性破乳剂WD-1加入点不合理。有2／3的含水原油在通过油水分离器之后才与破乳剂混合；二级沉降罐进油口伸入油相内，油流的冲击达不到中间层；WD-1对坨五站混合原油中的稠油破乳脱水性能欠佳，不能适应坨五站混合原油组成和含水的变化。针对上述各种原因筛选出了性能更好的一种破乳剂1916。根据确定的几种原因采取了相应的措施：将破乳剂加入点改在3个并联油水分离器之前；将二级沉降罐的进油口移到水相内；改用筛选出的破乳剂1916，结果使中间乳化层的增长受到了抑制。图2表4参2。     

Ensuring primary realization of pressure unit in the vacuum range without typically utilized static expansion system

After the break-up of Czechoslovakia in 1993 the primary metrological standards authority almost fully remained in Slovakia. So we had to build our primary vacuum metrology anew. But we could do it using uptodate techniques that are more effective and they enable us to fulfil our task more effectively and in a shorter time.The steady demand to widen the lower pressure range and a steady demand for maximal accuracy collide with the financial possibilities open to a small country. So it is impossible to follow the classical pattern for the vacuum standards: liquid columns, static expansion system and dynamic expansion system. But it is possible to utilize contemporary progress in construction of piston manometers. This enables us to discard liquid column and static expansion techniques in favour of piston technique [Tesar J, Prazak D. Vacuum 2002; 67: 311, Tesar J, Prazak D, Krajicek Z. In:Proceedings of international symposium on Pressure and Vacuum, 2003. p. 169, Tesar J, Repa P, Prazak D, Krajicek Z, Peksa L. Vacuum 2004; 76: 491.]. Such system fulfils all the needs of a little industrial country and is economically acceptable.     

Effect of C/Ti ratio on the laser ignited self-propagating high-temperature synthesis reaction of Al-Ti-C system for fabricating TiC/Al composites

TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al₃Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al₃Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized.     

KATRIN NEG pumping concept investigation

The Karlsruhe Tritium Neutrino experiment (KATRIN) is going to use a very large electro-static tandem spectrometer to measure the electron spectrum from the tritium beta decay, where several kilometers of non-evaporable getter (NEG) strips (type ST707) are to be used to achieve the UHV requirements. Different geometrical configurations of the NEG strips have been studied by Monte Carlo simulations. It is shown that the resulting pumping speed of the getter pumps will allow to get a pressure below 10⁻¹¹ mbar in the huge vessel with a volume of 1400 m³. By systematic assessment of the statistics of the pumping surfaces, it could be demonstrated that the design is sound.     

运用PLC技术改造385m~2凯利式叶滤机控制系统

根据生产实践 ,结合PLC的技术特点和 385m2 凯利式叶滤机的电气联锁特性 ,阐述了应用PLC技术 ,可进一步提高 385m2 凯利式叶滤机的运转率和自动化水平。     

Influence of Ni Interlayers on the Mechanical Properties of Ti6Al4V/(WC-Co) Friction Welds

Ni interlayers were introduced prior to dissimilar friction welding of Ti6Al4V base material to three cemented carbide substrates. The fracture strength of Ti6Al4V/(WC-6 wt% Co) welds were poor and were markedly improved when 20-µm thick Ni interlayers were introduced prior to dissimilar friction welding. These results were only produced when the (WC-6 wt% Co) cermet was electroplated prior to friction welding. When the Ti6Al4V alloy was electroplated prior to friction welding, fractured WC particles and cracking were observed in the (WC-Co) carbide substrate. The fracture strengths of Ti6Al4V/(WC-11 wt% Co) and Ti6Al4V/(WC-24 wt% Co) welds were not improved when 20-µm thick Ni interlayers were introduced prior to friction welding. During mechanical testing, the Ni layer retained at the dissimilar joint interface created a region of weakness.     

田5-斜19五段制剖面定向井钻井技术

五段制剖面定向井施工难度较大，主要介绍了田5—斜19井的井眼轨迹控制、相关安全钻井及钻井液技术，并对施工中发生的复杂情况进行了分析，总结了一些经验，对五段制剖面类型定向井施工具有一定的参考价值。