Ultrasound guided biopsy is a popular biopsy technology. An important issue for this technology is biopsy needle detection. However, the contrast of ultrasound images is low and the involved background is complicated. Existing needle detection methods cannot realize the fast and accurate needle detection. To address this issue, we have proposed a new needle detection algorithm by combining fuzzy enhancement with Hough transform. In the proposed method, the improved fuzzy enhancement method is firstly utilized to improve the image contrast, and image thinning algorithm is used to extract the linear skeleton. Then, Hough transform is adopted to detect the straight line. Finally, the endpoint detected using Hough transform is corrected based on the intensity correlation of pixels. The proposed method has been evaluated on the ultrasound prostate image sequences including 32 frames where each frame is of size 800×600. Experimental results demonstrate that the proposed method generally has higher detection accuracy than other compared methods in that it can provide 6.7% misdetection rate and its mean length and angle errors are 8.8 pixels and 0.98 degree, respectively. Meanwhile, the implementation time of the proposed method is 25 ms. Indeed, the proposed algorithm can detect the linear surgical instruments accurately and meet the demand of clinical practices.

When random disturbances are regularly introduced into a dynamical system over time, its small-signal stability is determined by the energy of perturbations accumulated in the system. To analyze this perturbation energy, this paper proposes a novel physically motivated Lyapunov modal analysis (LMA) framework, which combines selective modal analysis with the spectral decompositions of specially chosen Lyapunov functions. This approach allows the modal interactions in dynamical systems to be characterized and estimated in connection with specific state variables. Conventional participation factors characterize the relative contribution of the system modes and state variables to the evolution of states and modes, respectively. In contrast, the proposed Lyapunov participation factors characterize similar contributions to corresponding Lyapunov functions, which determine the integral energy associated with the states and modes on an infinite or finite time interval. This allows the estimation of modal interactions in terms of total energy produced by their mutual actions over time. Using a two-area four-machines power system, we demonstrate that LMA reliably identifies resonant modal interactions, merging of modes, and loss of stability, even for a linear model, and associates them with certain state variables. The Lyapunov participation factors corresponding to the selected part of the system spectrum can be calculated independently and serve as a basis for rapid real-time calculations of critical mode behaviors in large-scale dynamical systems.

The problem of the synthesis of a tracking system for electromechanical control objects is considered when measuring only the generalized coordinates of the mechanical subsystem. It is assumed that external and parametric perturbations act on the system. Assuming the smoothness of external perturbations and uncertainties, the mathematical model of the control object is presented in the form of a joint block form of controllability and observability relative to the coordinate basis of mixed variables (functions of state variables, external influences, and their derivatives). Based on these conditions of the joint block form of parametric uncertainty of the matrix before the control actions, a procedure for decomposition synthesis of the basic law of discontinuous control has been developed. The basic control law ensures exponential convergence of the generalized coordinates to the reference signals. To obtain estimates of the mixed variables used in the feedback, a method for synthesizing an observer of a lower order state with large coefficients is proposed, in which the principle of complete decomposition is implemented. The results of numerical modeling of the developed algorithms for a three-link manipulator operating in a cylindrical workspace under incomplete information conditions are presented.

Different forms of control problems for linear systems under essential uncertainty are considered. Specifically, three problems are examined. First, the unknown disturbances are assumed bounded and only their bounds are known. The problem is solved under various assumptions regarding the order of the disturbances and the observed signals, as well as the properties of the system. Second, the estimation of the unknown input (i.e., the inversion problem or the inverse problem) is considered. This problem is solved by the controlled model method with the control designed to stabilize the difference between the observed outputs of the original system and the model. Robust stabilization algorithms produce estimates of the unknown signals with a desired accuracy. The third problem focuses on stabilization of switched systems. The dynamics of the chosen system is described at each instant by one of the systems from a given finite set. Switching between regimes may depend both on time and on the system phase vector. Two problems are solved successively: finding stabilizers (a unique stabilizer if possible) for each plant from the family, and then investigating the conditions when switching between stable regimes does not disrupt the stability of the switched system. Various stabilization methods are obtained for switched systems covering different switching schemes.

We solve the output controller synthesis problem for multidimensional systems, guaranteeing the following parameters, either predefined or achievable: control errors, stability margin radius, and control time under the action of polyharmonic external disturbances with unknown amplitudes (with a limit on their sum), frequencies, and an unbounded number of harmonics. Our approach to solving the problem is based on a specially designed standard H-inf-optimization problem and a new rule for choosing a weight matrix for a given accuracy. For the first time, we give a physical interpretation of the stability margin radius of multidimensional systems in terms of Nyquist hodographs for individual contours that are open at the output of the object. We prove a connection between the absolute stability property of a closed system and the radius of stability margin. We consider the example of synthesis for an interconnected electric drive.