Input-output approach to robust stability and stabilization for uncertain singular systems with time-varying discrete and distributed delays

Based on input-output approach, the robust stability and stabilization problems for uncertain singular systems with time-varying delays are investigated. The parameter uncertainties are assumed to be norm-bounded and the time-varying delays include both discrete delay and distributed delay. By introducing a new input-output model, the time-delay system is embedded in a family of systems with a forward system without time delay and a dynamical feedback uncertainty. A sufficient and necessary condition, which guarantees the system regular, impulse-free and stable for all admissible uncertainties, is obtained. Based on the strict linear matrix inequality, the desired robust state feedback controller is also obtained. Finally, a numerical example is provided to demonstrate the application of the proposed method.

Research on Reliability of Knowledge-Updating in A Kind of Network Knowledge System

The definition of reliability of knowledge-updating in network knowledge resource management system (NKRM system for brief) has been given in this paper, which has important reference value to the evaluation of NKRM system. Besides, two kinds of models in NKRM system have been introduced. And one of the most common methods to improve reliability is the redundant technique. However, reliability and efficiency are inconsistent each other. By treating each knowledge as one part of the system, this paper proposes method of joint reserve of knowledge that may resolve this problem.

Modified onlay island flap versus tubularized incised plate urethroplasty for hypospadias reoperation

This study aimed to assess the outcomes of modified onlay island flap(MOIF)urethroplasty for hypospadias reoperation.A retrospective analysis was conducted using clinical data on children reoperated with MOIF or tubularized incised plate(TIP)urethroplasty for hypospadias in the Children's Hospital of Nanjing Medical University(Nanjing,China)from December 2016 to September 2020.A total of 90 children with hypospadias who failed primary repair and were reoperated on with MOIF(MOIF group,n=46)or TIP urethroplasty(TIP group,n=44)were recruited.All children were postoperatively followed up for at least 6 months.Six patients with postoperative urinary fistula,2 patients with glans dehiscence,and 1 patient with urethral diverticulum were reported in the MOIF group,while 7 patients with postoperative urinary fistula,2 patients with urethral stricture,and 1 patient with glans dehiscence were reported in the TIP group.Postoperative infection,flap necrosis and other complications were not recorded.A total of 37(80.4%)patients in the MOIF group and 34(77.3%)patients in the TIP group were successfully reoperated.Although the success rates of MOIF and TIP urethroplasty are comparable,pediatricians should master different types of repair techniques for individualized hypospadias reoperation.MOIF urethroplasty can be recommended after failure of the primary repair.

云环境下基于拟态防御的科学工作流执行系统（英文）

随着越来越多大规模科学计算任务交付云计算平台,云工作流系统被设计用于管理和安排这些复杂任务。然而,云计算中多租户共存服务模式存在严重安全风险,可能威胁云工作流的正常执行。为加强云工作流安全性,提出一种面向科学工作流的拟态云计算任务执行系统。拟态防御的思想主要涉及3个方面:异构性、冗余性和动态性。在异构性方面,集成物理服务器、管理器和操作系统的多样性以创建鲁棒的系统架构。在冗余性方面,工作流中每个子任务由多个执行体同时执行。综合考虑效率和安全性,提出滞后裁决机制检查任务执行结果。在动态性方面,设计动态任务调度机制切换工作流执行环境并缩短执行体生命周期,以混淆攻击者并净化任务执行体。实验结果表明,该系统有效增强了云工作流执行的安全性。

改进的变速率粒子滤波及其在机动目标跟踪中的应用(英文)

目的:针对一类特定的机动目标跟踪问题(目标长时间近似匀速直线运动,偶尔强机动运动),提出一种兼顾机动期间跟踪精度与非机动期间系统负担的非线性滤波方法。创新点:提出便于工程应用的基于笛卡尔坐标系的变速率模型和改进的变速率粒子滤波;提出机动检测方法而非多模型方法动态调整变速率粒子滤波的核心参数。通过在改进的变速率粒子滤波中嵌入无味粒子滤波,进一步改进估计精度。方法:首先,提出笛卡尔坐标系下的变速率采样模型。此时状态驻留时间不再与测量周期保持一致,从而可以减少目标非机动期间的状态更新次数。其次,提出一种基于机动检测的改进变速率粒子滤波方法,当目标机动或非机动时,动态调整变速率模型的Gamma分布参数。目标机动时,状态更新更频繁,粒子分布范围更广;目标非机动时,状态更新次数较少,降低系统存储和计算负担。最后,在改进的变速率粒子滤波中采用无味粒子滤波,进一步提高估计精度。结论:改进的变速率粒子滤波方法采用笛卡尔系而非本体坐标系,需要的先验信息更少,更便于工程应用。通过动态调整算法中的分布参数,采用无味粒子滤波方法,可以兼顾目标在非机动和机动期间的跟踪性能,同时降低系统的计算和存储负担。

Driftor: mitigating cloud-based side-channel attacks by switching and migrating multi-executor virtual machines

Co-residency of different tenants’ virtual machines(VMs) in cloud provides a good chance for side-channel attacks, which results in information leakage. However, most of current defense suffers from the generality or compatibility problem, thus failing in immediate real-world deployment. VM migration, an inherit mechanism of cloud systems, envisions a promising countermeasure, which limits co-residency by moving VMs between servers. Therefore, we first set up a unified practical adversary model, where the attacker focuses on effective side channels. Then we propose Driftor, a new cloud system that contains VMs of a multi-executor structure where only one executor is active to provide service through a proxy, thus reducing possible information leakage. Active state is periodically switched between executors to simulate defensive effect of VM migration. To enhance the defense, real VM migration is enabled at the same time. Instead of solving the migration satisfiability problem with intractable CIRCUIT-SAT, a greedy-like heuristic algorithm is proposed to search for a viable solution by gradually expanding an initial has-to-migrate set of VMs. Experimental results show that Driftor can not only defend against practical fast side-channel attack, but also bring about reasonable impacts on real-world cloud applications.

A novel onlay urethroplasty for hypospadias with mild chordee after degloving:modified for complete removal of scar tissue underlying the urethral plate and for long-term outcomes

Urethral plate(UP)-preserving urethroplasty is simple and has few complications,but it may affect the development of penis in the long term and lead to recurrent chordee.In this study,we used obliquely cut UP to repair hypospadias with mild chordee after degloving(15°-30°)and compared the results with onlay urethroplasty to explore its rationality and feasibility.Between April 2018 and October 2020,108 hypospadias patients underwent onlay urethroplasty or modified onlay urethroplasty.Clinical data were prospectively collected,and medium-term outcomes were assessed at follow-up.The complications were compared between the two groups.Forty-four patients underwent the modified onlay procedure(GroupⅠ),with follow-up time(mean±standard deviation[s.d.])of 23.2±4.5(range:17-31)months.Sixty-four patients underwent a standard onlay procedure(GroupⅡ),with follow-up time(mean±s.d.)of 39.7±3.9(range:32-46)months.There was no difference in age at surgery.The urethral defect length and operative time were longer in GroupⅠ.Six cases of fistula and one case each of stricture and diverticulum were reported in GroupⅠ.In GroupⅡ,11 cases of fistula and one case each of stricture and diverticulum were reported.The complication rates were 18.2%and 20.3%in GroupⅠand GroupⅡ,respectively(P>0.05).These medium-term follow-up results demonstrate that the modified onlay procedure(oblique cut UP urethroplasty)is a safe and feasible technique for hypospadias with mild chordee after degloving.Compared with standard onlay urethroplasty,this modified procedure is conducive to the complete removal of scar tissue underlying the UP without increasing the risk of surgical complications.