圆弧形联节齿轮加工方法研究

本文根据作者生产实践，摸索研究出一种简易、操作方便在在万能铣床或滚齿机上加工圆弧形联节齿轮的方法，解决了无专用设备加工圆弧形联节齿轮的难题，提出了在铣床上利用圆转台加工，在滚齿机用圆弧形靠模样板加工的方法和原理。实践证明，这两种方法加工圆弧形联节齿轮，同样能符合图纸规定的齿合要求，有一定实用价值，便于广泛推广。

完井卸联顶节时套管脱扣事故分析

针对完井卸联顶节过程中发生的两起事故进行了分析,详细说明了事故发生的原因和事故处理措施,并提出了相应的技术对策及建议。同时也希望能引起钻井技术人员和工程监督的重视,在工作中事无巨细严格按规程操作,避免事故发生。

LGZ-1500/Y型连铸连轧机安全联轴节结构的改进

针对LGZ-1500/Y型连铸连轧机在生产中安全联轴节保险销易断造成频繁停机的问题,从结构设计着手,对安全联轴节保险销结构加以改进,解决了保险销易断问题。

上海龙联汽车用品采购中心之车友文化节盛大开幕

日前，由上海龙联汽车用品市场倾力主办的“上海龙联车友文化节”在龙联盛大举行，为了迎接龙联汽车用品市场车友文化节的举办，市场协同各商家，做出了优惠的活动。据悉，龙联汽车用品采购中心已经正式开业一周年。

风机的传动调节与节能

简述了工业锅炉风机的传动联接、风量调节与节能降耗的关系，并通过实例进一步证明其提高锅炉热效率的效果是非常明显的。

φ139.7×7.72mm J55长圆螺纹套管脱扣原因分析

详细调查了套管脱扣事故情况,研究了脱扣套管的变形特征和螺纹损伤规律,分析了套管脱扣的原因,对套管材质进行了全面检测。模拟套管受力状况,对套管实物性能进行验证试验,认为套管脱扣原因并非过载所致,而是在卸连顶节过程中发生倒扣才发生套管脱扣事故的。

一种集成型高压隔离开关电动操作机构箱研制

高压隔离开关电动操作机构是发电厂、变电站中常用电气设备之一,使用量大,其性能和质量与电网安全运行和建设成本密切相关。作者在调研分析传统型高压隔离开关电动操作机构设计制造、安装调试及运行维护的基础上,通过优化结构,集成功能,采用新技术和工艺,研制出一种集成型高压隔离开关电动操作机构箱。1台集成型高压隔离开关电动操作机构箱同时可完成对隔离开关主刀、地刀的操作,具有结构简单、安装维护方便、机械连锁安全可靠、投资省等优点。本成果可应用于10kV及以上电压等级的高压隔离开关上,具有较好的经济效益和电力工程推广价值。

德国大众汽车公司的拯救者

1992年、1993年对德国大众汽车公司来说,是非常不景气的年份。仅去年一年公司就亏损近20亿马克,从而使这家世界闻名的汽车制造企业一度陷于低谷。 今年开始出现转机 但是,在时隔一年多的今天,大众汽车公司却出现了引人注目的转机。

Evolution of plant microRNA gene families

MicroRNAs （miRNAs） are important post-transcriptional regulators of their target genes in plants and animals, miRNAs are usually 20-24 nucleotides long. Despite their unusually small sizes, the evolutionary history of miRNA gene families seems to be similar to their protein-codingcounterparts. In contrast to the small but abundant miRNA families in the animal genomes, plants have fewer but larger miRNA gene families. Members of plant miRNA gene families are often highly similar, suggesting recent expansion via tandem gene duplication and segmental duplication events. Although many miRNA genes are conserved across plant species, the same gene family varies significantly in size and genomic organization in different species, which may cause dosage effects and spatial and temporal differences in target gene regulations. In this review, we summarize the current progress in understanding the evolution of plant miRNA gene families.

Belt or network?The spatial structure and shaping mechanism of the Great Wall cultural belt in Beijing

The relationship between cross-regional cultural landscapes does not currently receive enough attention in cultural landscape conservation. Cultural landscapes in China are faced with the crisis of fragmentation and islanding, which makes it necessary to strengthen the idea of integrated conservation. The Great Wall cultural belt in Beijing is a cross-regional linear cultural landscape in the northwest mountainous area of Beijing. With the Great Wall as a link connecting the surrounding natural, social, and cultural resources to form a banded structure, it has the typical and practical significance of integrated conservation. Based on the theory of the cultural landscape security pattern and its ‘node – setting – connection' model, this research studies the spatial structure and shaping mechanism of the Great Wall cultural belt in Beijing from the perspective of tourist flow, using Flickr geo-tagged photos and Wikiloc tracks. The results identify the core nodes and intermediate nodes of the Great Wall cultural belt in Beijing and show that it has a multicore, multi-group hierarchical nesting structure differing from the geographic space, which has groups following the evolution orbit of ‘linear string – circumnuclear star – complete network.' To explain the differences between the cultural association network(CAN) and the geospatial network(GSN), we find that the cultural associations between nodes rely on geophysical channels, including heritage corridors and traffic passages, as physical carriers, but the nodes' attraction and their setting elements, containing natural geography environments, settlements, administrative divisions, etc., change the channel resistance, so CAN and GSN present different characteristics. From the perspective of systematic and spatial network thoughts, this study has made an attempt to adopt new analysis and research methods to achieve the integrated conservation and inheritance of linear cultural landscapes in mountainous areas.

Dual antiplatelet therapy increases pocket hematoma complications in Chinese patients with pacemaker implantation

Objective To assess the prevalence of the bleeding complications in pacemaker implanted patients receiving different antiplatelet regimens, and the influence of each regimen on hospital stays after device implantation. Methods We prospectively enrolled 364 patients receiving the cardiac rhythm device implantations in Fuwai Hospital from July 2012 to December 2013. Bleeding complications including pocket hematoma, hemothorax, cardiac tamponade and blood transfusion requirement were measured as endpoints. Post operation hospital stay was also included in the endpoints. Results Bleeding complications were detected in 15 patients （14 with hematoma, one with hemothorax） out of all 364 patients （4.12%）. Dual antiplatelet therapy （DAT） significantly increased hematoma （19.3%） compared with aspi- fin treatment （ASA） （3.2%, P = 0.001） and no antiplatelet therapy （1.9%, P 〈 0.001）. There was no significant difference in incidence of pocket hematoma between the ASA group and the control group （P = 0.45）. The post procedure hospital stay was longer in DAT group （5.45 ± 2.01 days） compared to those in the ASA group （3.65 ± 1.37 days, P 〈 0.05） or control group （3.99 ± 2.27 days, P 〈 0.05）. Pocket hema- toma was considered an independent predictor of hospital stay prolongation （OR： 5.26; 95% CI： 1.56-16.64; P = 0.007）. Conclusions Among the Chinese patients undergoing device implantation in this study, the use of dual antiplatelet agents significantly increased the risk of pocket hematoma complications and led to a longer hospital stay. Use of aspirin alone did not increase the risk.

Elastodynamic modeling and joint reaction prediction for 3-PRS PKM

To gain a thorough understanding of the load state of parallel kinematic machines(PKMs), a methodology of elastodynamic modeling and joint reaction prediction is proposed. For this purpose, a Sprint Z3 model is used as a case study to illustrate the process of joint reaction analysis. The substructure synthesis method is applied to deriving an analytical elastodynamic model for the 3-PRS PKM device, in which the compliances of limbs and joints are considered. Each limb assembly is modeled as a spatial beam with non-uniform cross-section supported by lumped virtual springs at the centers of revolute and spherical joints. By introducing the deformation compatibility conditions between the limbs and the platform, the governing equations of motion of the system are obtained. After degenerating the governing equations into quasi-static equations, the effects of the gravity on system deflections and joint reactions are investigated with the purpose of providing useful information for the kinematic calibration and component strength calculations as well as structural optimizations of the 3-PRS PKM module. The simulation results indicate that the elastic deformation of the moving platform in the direction of gravity caused by gravity is quite large and cannot be ignored. Meanwhile, the distributions of joint reactions are axisymmetric and position-dependent. It is worthy to note that the proposed elastodynamic modeling method combines the benefits of accuracy of finite element method and concision of analytical method so that it can be used to predict the stiffness characteristics and joint reactions of a PKM throughout its entire workspace in a quick and accurate manner. Moreover, the present model can also be easily applied to evaluating the overall rigidity performance as well as statics of other PKMs with high efficiency after minor modifications.

Optical A/D Quantizer Scheme Based on Parallel Phase Mod ulators

A high-speed and high-resolution optical A/D quantizer is proposed.Its architecture is discussed.Bit circuits are built by using the phase modulators in parallel.Based on the different character of the half-wave voltage for every phase modulator and the polarized bias design of incident light,the RF input signal is coled and transmitted in the form of optical digital signal.According to the principle of the architecture,the high-resolution quantizers with 8-bit and 12-bit,et al.are built,which operate at 100 GS/s.Their quantization noise is invariable almost with bit circuits increasing.The simulation result of 4-bit A/D quantizer is also given.

Can coordination variability identify performance factors and skill level in competitive sport? The case of race walking

Background:Marginal changes in the execution of competitive sports movements can represent a significant change for performance success.However,such differences may emerge only at certain execution intensities and are not easily detectable through conventional biomechanical techniques.This study aimed to investigate if and how competition standard and progression speed affect race walking kinematics from both a conventional and a coordination variability perspective.Methods:Fifteen experienced athletes divided into three groups(elite,international,and national) were studied while race walking on a treadmill at two different speeds(12.0 and 15.5 km/h).Basic gait parameters,the angular displacement of the pelvis and lower limbs,and the variability in continuous relative phase between six different joint couplings were analyzed.Results:Most of the spatio-temporal,kinematic,and coordination variability measures proved sensitive to the change in speed.Conversely,non-linear dynamics measures highlighted differences between athletes of different competition standard when conventional analytical tools were not able to discriminate between different skill levels.Continuous relative phase variability was higher for national level athletes than international and elite in two couplings(pelvis obliquity—hip flex/extension and pelvis rotation—ankle dorsi/plantarflexion) and gait phases(early stance for the first coupling,propulsive phase for the second) that are deemed fundamental for correct technique and performance.Conclusion:Measures of coordination variability showed to be a more sensitive tool for the fine detection of skill-dependent factors in competitive race walking,and showed good potential for being integrated in the assessment and monitoring of sports motor abilities.

A New Route to the Interpretation of Hopf Invariant

We discuss an object from algebraic topology,Hopf invariant,and reinterpret it in terms of the φ-mappingtopological current theory.The main purpose of this paper is to present a new theoretical framework,which can directlygive the relationship between Hopf invariant and the linking numbers of the higher dimensional submanifolds of Euclideanspace R^(2n-1).For the sake of this purpose we introduce a topological tensor current,which can naturally deduce the(n-1)-dimensional topological defect in R^(2n-1) space.If these (n-1)-dimensional topological defects are closed orientedsubmanifolds of R^(2n-1),they are just the (n-1)-dimensional knots.The linking number of these knots is well defined.Using the inner structure of the topological tensor current,the relationship between Hopf invariant and the linkingnumbers of the higher-dimensional knots can be constructed.

Energy-Efficient Sensing and Transmission for Multi-Hop Relay Cognitive Radio Sensor Networks

How to achieve transmissions in an energy-efficient way in multi-hop decode and forward(DF) relay cognitive radio sensor networks(CRSNs) is important since sensor nodes in CRSNs are usually battery powered. This paper aims to maximize energy efficiency(EE) by joint optimizing sensing time and power allocation in multi-channels & multihops DF relay CRSNs under constraints on outage probability and sensing performance. First, we design a channel selection scheme for sensing according to the available probabilities of multi channels. Second, we analyze the expected throughput and energy consumption and formulate the EE problem as a concave/concave fractional program. Third, coordinate ascent and Charnes-Cooper Transformation(CCT) methods are used to transform the nonlinear fractional problem into an equivalent concave problem. Subsequently, the closed form of outage probability is derived and the convergence rate of the iterative algorithm is analyzed. Finally, simulation results show that the proposed scheme can achieve effective EE.

长螺旋输送机中间轴承的改进

将长螺旋输送机中间轴承联轴短节由刚性改为柔性,解决其经常断裂的问题,实际使用表明效果良好。

Temperature-flow regulation rule in indirect connection heating system and its energy-saving contrast analysis

Primary and secondary networks are treated as a whole in indirect heating systems, and an advanced new temperature-flow regulation method is presented whose flow ratio is greater than 60% in a secondary network and 30% in a primary network when under a partial load. Through deducing and optimizing an exponential function flow regulation rule, the formulae of flow regulation and the supply and return water temperatures are obtained, and their relevant curves are plotted. After comparison, it is found that this control method has a huge energy conservation space, and it should therefore be generalized soon.