用共关键词网络揭示领域知识结构的实验研究

本文利用Web of Science数据库，构建出数学、电化学、信息计量学和传播学4个领域的高频共关键词网络。用于反映领域核心知识。此类网络以关键词为节点，当两个关键词用于同一论文中时就形成节点之间的连接。核心／边缘分析和网络分析参数表明核心关键词数量增长速度低于关键词总量增速。依据核心关键词表达核心知识概念的逻辑，推论特定知识领域中稳定的核心概念及其共现网络反映了该领域相对稳定的核心知识及其结构。

新出现趋势识别和分析方法引介

新出现趋势是一个新研究论题深入研究并日趋重要的趋势。这种趋势在科学前沿形成,通过研究人员相互引用表现出来。检测这样的趋势所用的方法起源于引文分析。以前,引文分析仅仅是简单的静态的数量分析,而现在开始利用复杂网络分析和时间序列分析进行动态发展趋势预测。目前新出现趋势分析的方法主要有两种:一是从高引用文章组成的聚类串随时间推移的变化特征中检测出新出现趋势。二是在引文网络中所形成的研究社区中检测新出现趋势。目前新出现趋势分析还要在三个方面进行深入研究:一是要在实证研究充分开展的基础上,调查各个研究领域中新出现趋势的形成机制。二是要研究不同的时间序列对新出现趋势的识别和分析的影响。三是要研究新出现趋势对引文网络局部特征的影响。

基于一般P-C矩阵的R族科学发展节律指标——科学发展节律指标研究（1）

一论文集的一般P-C矩阵由论文数据和引文数据两部分组成。基于一般P-C矩阵并引入“等时性”概念，我们创建了关键变量Ck。Ck表示的是不同年份发表的论文在各自发表后第k年的引文数量的平均值。借助Ck可以构建R族科学发展节律指标，定义为引文观察值和引文期望值的比值，用于反映科学发展的节律。R族指标包括4项指标：①指标R——被引年视角加三角形引文窗口；②指标R’——被引年视角加平行四边形引文窗口；③指标r——引用年视角加三角形引文窗121；④指标r’——引用年视角加平行四边形引文窗口。以Journal of Documentation为例，本文具体说明了R族序列的计算和R族指标的应用。

远端器官预缺血改善冠状动脉缺血再灌注时心肌血供及减少心律失常发生率

远端器官缺血性预处理 (RPC)可减少缺血再灌注后心肌坏死范围。本研究旨在观察RPC对缺血再灌注心脏不同部位血流及心律失常发生率的影响。方法 :19头成年绵羊随机分为对照组 (n =9)及RPC组 (n =10 )。RPC组动物接受 3次左侧股动脉阻断 (5min)及再灌注 (5min) ,随后两组动物均分别依次阻断左冠状动脉前降支 (LAD) 10min ,再灌注 10min ;左冠状动脉第一分支 (D1)阻断及再灌注 10min后阻断左旋支 (LCX) 10min ,再灌注后观察 12 0min。结果 :LCX再灌注 10min时RPC组左室心内膜前壁、间隔及心外膜间隔心肌血流量 (分别为 0 .86± 0 .2 7,1.10±0 .34及 1.2 0± 0 .5 1ml·min-1·g-1)显著高于对照组 (分别为 0 .6 4± 0 .2 8,0 .6 9± 0 .2 3及 0 .5 8± 0 .2 6ml·min-1·g-1) ,P <0 .0 5。RPC显著减少再灌注后心室纤颤的发生率 (对照组 8/ 9,RPC组 2 / 10 ,P <0 .0 1)。冠状动脉阻断及再灌注后对照组主动脉平均压低于RPC组 ,但差异无显著性 (P >0 .0 5 )。结论 :RPC显著减少心肌缺血及再灌注期心室纤颤的发生 ,其机制可能与RPC显著改善心内膜血液供应有关。

远端器官缺血性预处理对心血管功能的影响

目的 :观察远端器官缺血性预处理 (RPC)对非缺血心脏功能的影响 ,初步探讨 RPC的作用机制。方法 :19只成年绵羊麻醉后随机分为对照组 (n=9)及 RPC组 (n=10 )。测定基础状态 (BS1 )各参数后 ,RPC组动物经历 3次左侧股动脉阻断 5 min及再灌注 5 m in,第三次再灌注后 10 min测 RPC后 (BS2 )各参数。对照组动物不阻断股动脉 ,但于相应时间测定 BS1 及 BS2 各参数。结果 :对照组 BS1 及 BS2 各参数无显著变化。 RPC显著降低平均动脉压(MAP)、外周血管阻力 (SVR)及冠脉循环阻力 (CVR) (P<0 .0 5 ) ;轻度增加心排出量及冠脉血流量 (P>0 .0 5 )。但RPC对心率、左房压、每搏输出量、射血分数及每搏作功无显著影响。 BS2 时 RPC组左室收缩末期压 (L VESP)、左室压力上升及下降最大速率 (± dp/ dtmax)、动脉有效弹回性 (Effective arterial elastance,Ea)均显著低于对照组 (P<0 .0 5 ) ,而心脏收缩及舒张期左室容积下降及增加最大速率 (± dv/ dtmax)无显著变化。结论 :远端器官缺血性预处理降低动脉有效弹性及循环阻力、减弱心脏收缩性的同时 ,并不减弱反而轻度增强心脏泵血功能 ,提高了心肌收缩效率。

衍生的P-C矩阵与扩散的R族科学发展节律指标——科学发展节律指标研究Ⅱ

本文是“基于一般P-C矩阵的R族科学发展节律指标”研究工作的继续。由一般P-C矩阵可以衍生出均值P-C矩阵，标准化P-C矩阵和标准化均值P-C矩阵。论文介绍了三种衍生矩阵的具体构造方法。基于三种衍生矩阵可以分别构建如、嘏和nRa族科学发展节律指标。依据考查视角是发文年还是引文年每族节律指标可以分为两组，每组包括两个指标，一个指标是基于三角形引文窗口定义的，另一指标基于平行四边形引文窗口。所有科学发展节律指标都是观察值与期望值比值的时间序列。论文还比较了R、Ra、nR和nRa族指标的特征，并以国际知名期刊《Sdence》为例讨论了四族节律指标的应用。

Effects of Cu-Wire Surface Fluctuations on Early Failures

Different chemical mechanical polishing （CMP） slurries are used to obtain single-damascene Cu-wires with different surface fluctuations as well as pre-existing surface-defects in wires with rougher surfaces. The presence of such pre-existing defects strongly increases the rate of early failures to almost 100%, reduces electromigration lifetime rapidly to the level of early failures, and changes the multimodal failure distribution into monomodal. The activation energy （0. 74±0.02eV） for the failure mechanism associated with these pre-existing defects confirms a dominant surface diffusion. It shows how a weakest link approximation analysis can he applied to a single wire by dividing the wire into relevant segments and assigning different failure mechanisms to the various segments. The analysis confirms that, although surface-defects are not the fastest early failure mechanism, the ten times higher surface-defectdensity in the rougher wires is responsible for the observed high early-failure rate and unreliable performance.

湿热环境中育成猪的体温节律研究(英文)

试验选用相同品种和体重的 4头育成猪 ,在适宜的环境中饲养一周后 ,将其中 2头猪置于湿热环境中 ,应用 DSI动物生理参数无线遥测系统研究了猪的体温节律性 .结果表明 :湿热环境下猪的体温和心率昼夜节律发生了明显变化 ,猪的体温最高并非出现在 16 :0 0～ 17:0 0 ,而是出现在 2 2 :0 0～ 2 3:0 0 ,且 2 4 h内体温差达 1.17℃ ;而猪的心率在 2 4 h内无昼夜差异 。

Prediction of vibrations from underground trains on Beijing metro line 15

The impact of vibrations due to underground trains on Beijing metro line 15 on sensitive equipment in the Institute of Microelectronics of Tsinghua University was discussed to propose a viable solution to mitigate the vibrations.Using the state-of-the-art three-dimensional coupled periodic finite element-boundary element(FE-BE) method,the dynamic track-tunnel-soil interaction model for metro line 15 was used to predict vibrations in the free field at a train speed of 80 km/h.Three types of tracks(direct fixation fasteners,floating slab track and floating ladder track) on the Beijing metro network were considered in the model. For each track,the acceleration response in the free field was obtained.The numerical results show that the influence of vibrations from underground trains on sensitive equipment depends on the track types.At frequencies above 10 Hz,the floating slab track with a natural frequency of 7 Hz can be effective to attenuate the vibrations.

On indexing in the Web of Science and predicting journal impact factor

We discuss what document types account for the calculation of the journal impact factor （JIF） as published in the Journal Citation Reports （JCR）. Based on a brief review of articles discussing how to predict JIFs and taking data differences between the Web of Science （WoS） and the JCR into account, we make our own predictions. Using data by cited-reference searching for Thomson Scientific＇s WoS, we predict 2007 impact factors （1Fs） for several journals, such as Nature, Science, Learned Publishing and some Library and Information Sciences journals. Based on our colleagues＇ experiences we expect our predictions to be lower bounds for the official journal impact factors. We explain why it is useful to derive one＇s own journal impact factor.

Open and robotic radical prostatectomy

Open retropubic radical prostatectomy has been the“gold standard”treatment for locally confined prostate cancer(PCa)but in recent years minimal invasive techniques as laparoscopy and robot-assisted prostatectomy have become widely available.The trifecta of the surgical treatment of PCa is cancer control,the preservation of continence,and erectile potency.Over the years the complication rates of radical prostatectomy have become very limited with improved cancer control and better functional results.We review the indications and the surgical technique of radical prostatectomy,be it open or laparoscopic,eventually robot-assisted as well as the pre-and postoperative measures and the surgery-related consequences.

Improved H-infinity channel estimator based on EM for MIMO-OFDM systems

H-infinity estimator is generally implemented in timevariant state-space models, but it leads to high complexity when the model is used for multiple input multiple output with orthogo- hal frequency division multiplexing （MIMO-OFDM） systems. Thus, an H-infinity estimator over time-invariant system models is pro- posed, which modifies the Krein space accordingly. In order to avoid the large matrix inversion and multiplication required in each OFDM symbol from different transmit antennas, expectation maximization （EM） is developed to reduce the high computational load. Joint estimation over multiple OFDM symbols is used to resist the high pilot overhead generated by the increasing number of transmit antennas. Finally, the performance of the proposed estimator is enhanced via an angle-domain process. Through performance analysis and simulation experiments, it is indicated that the pro- posed algorithm has a better mean square error （MSE） and bit error rate （BER） performance than the optimal least square （LS） estimator. Joint estimation over multiple OFDM symbols can not only reduce the pilot overhead but also promote the channel performance. What is more, an obvious improvement can be obtained by using the angle-domain filter.

髋关节整体替代陶瓷材料(英文)

许多材料在医学领域应用广泛,例如,整体替换硬组织或软组织的元件(如骨盆、骨头、关节、植牙等)、修补、诊断或矫正仪器(如起搏器、心脏阀等)。这些材料不仅要有好的力学性能,还要保持长期稳定,不能与人体相排斥。由于陶瓷材料在生理环境中具有强度高、生物相容性强和稳定性好的优点,人们研究用陶瓷材料替换骨骼。从20 世纪70 年代起,欧洲人用陶瓷组件置换整个髋关节。这些组件主要由氧化铝和氧化锆单体制成。然而,在有水环境中,氧化锆会发生低温降解。目前人们的研究重点在于提高陶瓷组件的强度和耐磨性,同时缩小其尺寸并延长其使用寿命。研究中使用的材料是氧化锆增韧的氧化铝复合陶瓷和其它氧化铝复合陶瓷,不再是单体陶瓷。另外,还可以使用氧化铝和氧化锆功能梯度复合材料。该梯度材料可以利用电泳沉积法(EPD)制得,其表面为纯氧化铝,中心部分为均匀的氧化铝、氧化锆复合材料,中间过渡部分是呈连续梯度渐变的氧化铝、氧化锆复合材料,烧成后会产生剩余热应力。设计这样的梯度结构是为了使复合材料具有最大表面压应力和最小内部张应力,与纯氧化铝组件相比,提高了强度和耐磨性。

网络信息检索中利用the Staceys测度方法提高逻辑运算效率的思考

网络信息检索中，逻辑运算符AND连接检索词的顺序很大程度上会影响检索效率。论文首先分析、介绍了the Staceys测度方法在改善AND检索效率中发挥的作用，并在此基础上提出简化了的测度算法，最后通过实例说明其实现步骤。

感染性心内膜炎的变化的流行病学和6个月死亡率的预测因素:一项前瞻性队列研究

目的：分析感染性心内膜炎（IE）的流行病学、最佳治疗和6个月死亡率的预测因素。方法和结果：此项前瞻性观察队列研究纳入了193例患者，在这些患者中有203次根据Duke修订标准确诊的IE发作。34％的发作与人工瓣膜有关；33％为院内感染；43％为葡萄球菌感染，26％链球菌感染，17％肠球菌感染。79％的发作至少出现一种并发症，63％行手术干预。6个月死亡率为22％：葡萄球菌感染者中为33％，肠球菌感染者为24％，链球菌感染者为8％。有手术禁忌证患者的死亡率为74％，而无手术禁忌证的药物治疗者为7％，手术治疗者为16％。

Multi-user Motion JPEG2000 over wireless LAN: run-time performance-energy optimization with application-aware cross-layer scheduling

This paper introduces a video application-aware cross-layer framework for joint performance-energy optimization,considering the scenario of multiple users upstreaming real-time Motion JPEG2000 video streams to the access point of a WiFi wireless local area network and extends the PHY-MAC run-time cross-layer scheduling strategy that we introduced in (Mangharam et al., 2005; Pollin et al., 2005) to also consider congested network situations where video packets have to be dropped. We show that an optimal solution at PHY-MAC level can be highly suboptimal at application level, and then show that making the cross-layer framework application-aware through a prioritized dropping policy capitalizing on the inherent scalability of Motion JPEG2000 video streams leads to drastic average video quality improvements and inter-user quality variation reductions of as much as 10 dB PSNR, without affecting the overall energy consumption requirements.

Channel adaptive rate control for energy optimization

Low energy consumption is one of the main challenges for wireless video transmission on battery limited devices. The energy invested at the lower layers of the protocol stack involved in data communication, such as link and physical layer, represent an important part of the total energy consumption. This communication energy highly depends on the channel conditions and on the transmission data rate. Traditionally, video coding is unaware of varying channel conditions. In this paper, we propose a cross-layer approach in which the rate control mechanism of the video codec becomes channel-aware and steers the instantaneous output rate according to the channel conditions to reduce the communication energy. Our results show that energy savings of up to30% can be obtained with a reduction of barely 0.1 dB on the average video quality. The impact of feedback delays is shown to be small. In addition, this adaptive mechanism has low complexity, which makes it suitable for real-time applications.

Impact of bolus volume on small intestinal intra-luminal impedance in healthy subjects

AIM: To assess the impact of bolus volume on the characteristics of small intestinal (SI) impedance signals.METHODS: Concurrent SI manometry-impedance measurements were performed on 12 healthy volunteers to assess the pattern of proximal jejunal fluid bolus movement over a 14 cm-segment.Each subject was given 34 boluses of normal saline (volume from 1 to 30 mL) via the feeding tube placed immediately above the proximal margin of the studied segment.A bolus-induced impedance event occurred if there was > 12% impedance drop from baseline,over ≥ 3 consecutive segments within 10 s of bolus injection.A minor or major imped-ance event was defined as a duration of impedance drop < 60 s or ≥ 60 s,respectively.RESULTS: The minimum volume required for a detectable SI impedance event was 2 mL.A direct linear relationship between the SI bolus volume and the occurrence of impedance events was noted until SI bolus volume reached 10 mL,a volume which always produced an impedance flow event.There was a moderate correlation between the bolus volume and the duration of impedance drop (r = 0.63,P < 0.0001) and the number of propagated channels (r = 0.50,P < 0.0001).High volume boluses were associated with more major impedance events (≥ 10 mL boluses = 63%,3 mL boluses = 17%,and < 3 mL boluses = 0%,P = 0.02).CONCLUSION: Bolus volume had an impact on the type and length of propagation of SI impedance events and a threshold of 2 mL is required to produce an event.

Superelastic behavior and stabilization of stress-induced martensite in Cu-13.4Al-4.0Ni single crystals

By applying tensile stress along 〈100〉 of β phase, the superelastic behavior and stabilization of stress induced martensite (SIM) of Cu 13.4Al 4.0Ni(mass fraction, %) single crystals were studied. The results show that the pseudo yield stress decreases with the increase of cycling number, and keeping load isothermally has an effect on stabilization of SIM. Previous thermal cycling between ( M s-20 ℃) and ( A f+20 ℃) promotes the superelasticity and the stabilization of SIM as well; the pre thermal cycling also reduces the pseudo yield stress. However, once the stabilization of SIM is produced, it can be destabilized by either the afterwards thermal cooling heating cycling or load and immediately unload cycling in ( A f～ M d). Isothermal treatment in ( A f～ M d) brings restabilization of SIM. The maximum superelastic value from β → β ′ 1(18 R ) is 9% for the studied single crystal. When test temperature is in A f～( A f+50 ℃) and stress is in 0～350 MPa, the superelastic behavior exist. [