Optimal guaranteed cost stabilization of networked systems with bounded random packet losses

This paper is concerned with the optimal guaranteed cost stabilizing controller design problem for a class of networked control systems (NCSs) with random packet losses. The number of consecutive packet losses is assumed to be upper bounded, and the closed‐loop NCS is described as a discrete‐time stochastic delay system with a time‐varying input delay and a stochastic parameter. A sufficient condition is derived for the closed‐loop NCS to be exponentially stable and achieve an optimal guaranteed cost performance level. The relationships among the exponential decay rate, the guaranteed cost performance level, and two parameters characterizing the random packet losses, namely, the packet loss probability and the maximal number of consecutive packet losses, are simultaneously established in the obtained condition. Furthermore, design procedures for the state feedback stabilizing controllers are also presented. Finally, an illustrative example is given to show the effectiveness of the proposed results. Copyright © 2011 John Wiley & Sons, Ltd.     

肘关节内侧副韧带前束重建的生物力学研究

目的通过测量肘关节内侧副韧带(medial collateral ligament,MCL)前束生物力学指标,探讨前束完整及重建后对肘关节外翻稳定性的影响,评价采用人工肌腱、界面螺钉重建MCL前束疗效。方法成人完整上肢标本12具,男8具,女4具;左、右侧各6具;制成肘关节"骨-韧带"标本。采用生物力学及压敏胶片测量方法,分别测量MCL前束完整(对照组)及使用人工肌腱、界面螺钉重建后(实验组)肘关节屈曲0、30、60、90°时关节外翻松弛度、肱尺关节受力面积及肘关节内压强。结果两组在肘关节不同屈曲角度下,组内及组间关节松弛度比较,差异均无统计学意义(P>0.05)。除肘关节屈曲0°时两组肘关节压强小于其余屈曲角度(P<0.05),及对照组小于实验组(P<0.05)外,两组其余各角度组内及组间比较差异均无统计学意义(P>0.05)。除对照组内肘关节屈曲0°时肱尺关节受力面积大于其余屈曲角度(P<0.05)外,两组其余各角度组内及组间比较差异均无统计学意义(P>0.05)。结论 MCL前束对维持肘关节外翻稳定性具有重要意义,金属界面螺钉加人工肌腱重建后可即刻恢复内侧稳定。     

重建椎体完整性和稳定性在胸腰椎骨折中的应用

目的探讨胸腰段骨折重建椎体完整性和稳定性的方法及临床意义。方法 35例胸腰椎骨折全部行后路椎体撑开复位病椎内植骨联合RF短节段内固定手术,平均15个月取出内固定。结果 35例患者平均随访19个月,X线片示全部骨性愈合,即刻矫正满意,远期矫正无丢失,采用F ranke l脊髓损伤分级进行神经功能评定有不同程度的恢复。结论胸腰段骨折经伤椎椎弓根椎体撑开复位椎体内植骨联合RF内固定以重建椎体的完整性和稳定性,可有效防止矫正度丢失、内固定松动断裂、晚期脊柱不稳及继发椎管狭窄等并发症,而且创伤小,效果可靠,操作简便。     

The effect of overlapping on the primary stability of osteochondral grafts in mosaicplasty

Our goal was to determine the primary stability of overlapping osteochondral grafts used in mosaicplasty by studying the effect of overlapping in an ex vivo model. Osteochondral grafts, 10 mm in diameter, were transplanted from the trochlea of cow femurs to the weight-bearing area of the lateral femoral condyle with 0, 15, or 30% overlap. The grafts were pushed in with a probe at a rate of 2 mm/min, and load (N)-displacement (mm) curves were recorded. In Group I (control, 0% overlap), insertion 1 and 2 mm below the cartilage level could be reached at 572.3 +/- 273.6 and 999.3 +/- 427.6 N, respectively. In Group II (15% overlap), insertion 1 and 2 mm below the cartilage level could be reached at 263.6 +/- 91.7 and 746.6 +/- 88.0 N, respectively. In Group III (30% overlap), insertion 1 and 2 mm below the cartilage level could be reached at 179.4 +/- 31.2 and 657.0 +/- 106.5 N, respectively. The loads that were necessary to produce a 1-mm dent in the grafts were significantly different between Groups I and II and Groups I and III (p < 0.05). These results suggest that stability may be reduced by graft overlapping in mosaicplasty surgery. The results of this ex vivo animal study contribute to a more complete understanding of the primary stability of osteochondral grafts in an overlapping position as well as postoperative protocols.     

Optimal control strategy–based AGC of electrical power systems: A comparative performance analysis

This study extensively addresses the application of optimal control approach to the automatic generation control (AGC) of electrical power systems. Proportional‐integral structured optimal controllers are designed using full‐state feedback control strategy employing performance index minimization criterion. Some traditional single/multiarea and restructured multiarea power system models from the literature are explored deliberately in the present study. The dynamic performance of optimal controllers is observed superior in comparison to integral/proportional‐integral controllers tuned using some recently published modern heuristic optimization techniques. It is observed that optimal controllers show better system results in terms of minimum value of settling time, peak overshoot/undershoot, various performance indices, and oscillations corresponding to change in area frequencies and tie‐line powers along with maximum value of minimum damping ratio in comparison to other controllers. The results are displayed in the form of tables for ease of comparison. Sensitivity analysis affirms the robustness of the optimal feedback controller gains to wide variations in some system parameters from their nominal values.     

Numerical Stability Analysis for a Stationary and Translating Droplet at Extremely Low Viscosity Values Using the Lattice Boltzmann Method Color-Gradient Multi-Component Model with Central Moments Formulation

Multicomponent models based on the Lattice Boltzmann Method (LBM) have clear advantages with respect to other approaches, such as good parallel performances and scalability and the automatic resolution of breakup and coalescence events. Multicomponent flow simulations are useful for a wide range of applications, yet many multicomponent models for LBM are limited in their numerical stability and therefore do not allow exploration of physically relevant low viscosity regimes. Here we perform a quantitative study and validations, varying parameters such as viscosity, droplet radius, domain size and acceleration for stationary and translating droplet simulations for the color-gradient method with central moments (CG-CM) formulation, as this method promises increased numerical stability with respect to the non-CM formulation. We focus on numerical stability and on the effect of decreasing grid-spacing, i.e. increasing resolution, in the extremely low viscosity regime for stationary droplet simulations. The effects of small- and large-scale anisotropy, due to grid-spacing and domain-size, respectively, are investigated for a stationary droplet. The effects on numerical stability of applying a uniform acceleration in one direction on the domain, i.e. on both the droplet and the ambient, is explored into the low viscosity regime, to probe the numerical stability of the method under dynamical conditions.     

选择性骶骨切除对骨盆生物力学稳定性的影响

目的用生物力学测试的方法分析新鲜人骨盆模型不同骶骨平面切除对骨盆稳定性的影响。方法选用8具男性新鲜尸体L5-骨盆标本,平稳加载至1 000 N,对各个测试点保留完整骶骨及不同平面骶骨切除骨盆模型的剪切应力、最大主应力、位移及刚度变化依次测试,并比较各组间的差异。进行骨盆环的测量,记录骨折部位和骨折类型。结果随着骶骨切除平面的增高,各个测试点的剪切应力、最大主应力及骶骨下沉位移均有不同程度增大,骨盆的轴向刚度逐渐减小。当切除平面到达S_1时变化明显,尤以经过1/4 S_1组、1/2S_1组变化显著,与S_0组比较差异均有统计学意义(P0.05)。结论骶骨的切除范围与骨盆的生物力学稳定性密切相关,残留骶髂关节各种应力随着骶骨切除平面升高而急剧增高,骨盆的稳定性明显下降。当骶骨切除到S_1椎体时,极易发生骨折,需要通过腰骶髂局部重建的方式增强骶髂关节的稳定性。     

四种螺纹截面形态对种植体初期稳定性影响的三维有限元研究

目的 利用即刻负载有限元模型研究种植体不同螺纹截面类型因素对初期稳定性的影响.方法 利用Pro/E软件、Hypermesh 7.0软件及ABAQUS 6.5有限元软件,建立4类种植体即刻负载的三维有限元模型,比较4种螺纹截面形态(V型,支撑型, 矩型和反支撑型)在分别垂直和水平加载时对种植体初期稳定性的影响.结果 对不同螺纹截面形态种植体的微动程,垂直加载时支撑型螺纹种植体微动最小,反支撑型螺纹种植体微动最大,水平加载时反支撑型螺纹种植体微动最小,支撑型螺纹种植体微动最大.结论 螺纹截面的形态和强度对垂直相对位移有影响, 对颊舌相对位移影响不大,螺纹顶边和底边与种植体体部的角度越大,抵抗垂直向的能力越强,但强度差,因此在螺纹种植体设计时,要兼顾螺纹截面角度和强度.     

Laser-induced thermal injury to dermal blood vessels: analysis of wavelength (585 nm vs. 595 nm), cryogen spray cooling, and wound healing effects

BACKGROUND AND OBJECTIVES: Successful laser treatment of cutaneous hyper-vascular lesions requires appropriate laser irradiation parameters for selective photothermolysis of ectatic dermal blood vessels as well as appropriate cooling parameters for epidermal protection based on an individual patient basis. Using the rabbit ear as an in vivo model for dermal vasculature, we investigated the influences of laser wavelength (585 nm vs. 595 nm) and cryogen spray cooling with various spurt durations on the laser-induced thermal injury to dermal blood vessels. Wound healing response was also evaluated in 2 hours and 4 days. STUDY DESIGN/MATERIALS AND METHODS: Flashlamp-pumped pulsed dye laser ScleroPlus (operated at the wavelength of 585 or 595 nm) was used for the comparison between the influences of two wavelengths (585 nm vs. 595 nm). R134-a cryogen spurts with the durations from 50 to 300 milliseconds were sprayed onto the sites to be irradiated and terminated 20 milliseconds before the onset of the laser pulses. In vivo rabbit ear was used as the model for cutaneous hyper-vascular lesions. Totally 10 New Zealand Albino white rabbits were experimented and in each rabbit ear six to seven sites were irradiated. Five animals were sacrificed 2 hours after the irradiation, and the remaining five sacrificed 4 days after the irradiation. Thermal injury to the blood vessel was assessed by hematoxylin and eosin stained histological sections and confirmed by an apoptosis assay. RESULTS: When the radiant exposures were above 10 J/cm2, 595 nm wavelength induced equivalent or more severe thermal injury to dermal blood vessels than 585 nm. Cryogen spray cooling with the spurt durations above 100 milliseconds resulted in increased depth of the most superficial thermal injury to dermal blood vessels than without cooling, indicating that superficial blood vessels were non-specifically cooled by the cryogen spurts applied at these parameters. Laser-induced thermal injury was significantly healed in the rabbit ear vasculature at 4 days post irradiation. CONCLUSIONS: Given sufficient radiant exposure, 595 nm wavelength can induce equivalent or more severe vascular injury compared with 585 nm. Cryogen spray cooling with the spurt durations above 100 ms may impair the photocoagulation of superficial blood vessels. Irreversible thermal injury to blood vessel can be achieved only when the basement membrane of blood vessel wall is irreversibly damaged.