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排序方式: 共有491条查询结果,搜索用时 15 毫秒
31.
Vascular disease produces changes in lumenal shape evident in magnetic resonance angiography (MRA). However, quantification of vascular shape from MRA is problematic due to image artifacts. Prior deformable models for vascular surface reconstruction primarily resolve problems of initialization of the surface mesh. However, initialization can be obtained in a trivial manner for MRA using isosurfaces. We propose a methodology for deforming the isosurface to conform to the boundaries of objects in the image with minimal a priori assumptions of object shape. As in conventional methods, external forces attract the surface toward edges in the image. However, smoothing is produced by a moment that aligns the normals of adjacent surface triangles. Notably, the moment produces no translational motion of surface triangles. The deformable isosurface was applied to a digital phantom of a stenotic artery, to MRA of three renal arteries with atherosclerotic disease and MRA of one carotid artery with atherosclerotic disease. Results of the surface reconstruction from the deformable model were compared with conventional X-ray angiography for the renal arteries. Measurement of the degree of stenosis of the renal arteries was within 12% +/- 6%. The deformable model provided improvements over the isosurface in all cases in terms of measurement of the degree of stenosis or improving the surface smoothness. 相似文献
32.
Jeong-Ryeol Kim Geun-Kyu Choi Dong Kyun Yim Jong-Sung Park Kug Sun Hong 《Journal of Electroceramics》2006,17(1):65-69
Glasses in the ZnO-B2O3-MO3(M = W, Mo) ternary were examined as potential replacements to PbO-B2O3-SiO2-ZnO glass frits with the low firing temperature (500–600∘C) for the dielectric layer of a plasma display panels (PDPs). Glasses were melted in air at 950–1150∘C in a narrow region of the ternary using standard reagent grade materials. The glasses were evaluated for glass transition
temperature (T
g
), softening temperature (T
d
), the coefficient of thermal expansion (CTE), dielectric constant (ε
r
), and optical property. The glass transition temperature of the glasses varied between 470 and 560∘C. The coefficient of thermal expansion and the dielectric constant of the glasses were in the range of 5–8 × 10− 6/∘C and 8–10, respectively. The addition of MO3to ZnO-B2O3binary could induce the expansion of glass forming region, the reduction of T
g
and the increase in the CTE and the dielectric constant of the glasses. Also, the effect of the addition of MO3to ZnO-B2O3binary on the transmittance in the visible-light region (350–700 nm) was investigated. 相似文献
33.
Yuxiang Mo Sitaram Aryal Paul Rulis Wai‐Yim Ching 《Journal of the American Ceramic Society》2014,97(8):2646-2653
The term “MAX phase” refers to a very interesting and important class of layered ternary transition‐metal carbides and nitrides with a novel combination of both metal and ceramic‐like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. Using (Cr2Hf)2Al3C3 as an example, we demonstrate the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of MAX phase‐like (Cr2Hf)2Al3C3 are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry (P63/mmc, #194), (Cr2Hf)2Al3C3 crystallizes in the monoclinic space group of P21/m (#11) with lattice parameters of a = 5.1739 Å, b = 5.1974 Å, c = 12.8019 Å; α = β = 90°, γ = 119.8509°. Its structure is found to be energetically much more favorable with an energy (per formula unit) of ?102.11 eV, significantly lower than those of the allotropic segregation (?100.05 eV) and solid solution (?100.13 eV) phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that (Cr2Hf)2Al3C3 has outstanding elastic moduli. 相似文献
34.
Haiping Du James Lam Kam Yim Sze 《Engineering Applications of Artificial Intelligence》2003,16(7-8):667-680
This paper presents an approach to design static output feedback and non-fragile static output feedback H∞ controllers for active vehicle suspensions by using linear matrix inequalities and genetic algorithms. A quarter-car model with active suspension system is considered in this paper. By suitably formulating the minimization problem of the sprung mass acceleration, suspension deflection and tyre deflection, a static output feedback H∞ controller and a non-fragile static output feedback H∞ controller are obtained. The controller gain is naturally constrained in the design process. The approach is validated by numerical simulation which shows that the designed static output feedback H∞ controller can achieve good active suspension performance in spite of its simplicity, and the non-fragile static output feedback H∞ controller has significantly improved the non-fragility characteristics over controller gain variations. 相似文献
35.
An Yong Lee Jongguk Yim Youngjin Choi 《International Journal of Control, Automation and Systems》2014,12(5):1102-1109
This paper presents a scaled Jacobian transpose based control method for robotic manipulators as a modification of a conventional Jacobian transpose based method. The proposed method has several advantages such as it shows faster convergence and better tracking performance than the conventional method, furthermore, it does not have any singularity problem similar to the conventional method. The scaled Jacobian transpose is obtained by collecting each pseudoinverse of the column vector of the Jacobian matrix. The proposed method performs a given task well under singular configurations while minimizing the task error. Finally, a few comparative studies with the conventional method are provided to show the effectiveness of the proposed method through simulations. 相似文献
36.
The question of realization and feedback linearization of a class of differential-algebraic system is considered. Based on nonlinear inversion of an input-output map, an analytical expression for the constraint force vector satisfying the algebraic constraints is derived. In this derivation, certain requirements on the relative degree of the output variables are relaxed. Using a new representation of the system in an extended state space, a control law is derived for the independent control of the chosen output variables satisfying algebraic constraints. These results are applied for the position and force control of robotic manipulators. Simulation results are presented for a three-link robotic arm with revolute joints. It is shown that in the closed-loop system, precise position and force trajectory control is accomplished in spite of uncertainty in the robot parameters. 相似文献
37.
Sehyuk Yim Doyoung Jeon 《International Journal of Control, Automation and Systems》2014,12(2):383-389
This paper proposes a magnetic mechanical capsule robot which crawls in a fluid-filled tube. The developed capsule robot employs two locomotion mechanisms simultaneously. It has spiral ribs at both ends, which are rotated by a small on-board motor. Such rotating spiral structures generate a driving force of the capsule robot. We invented a magnetic mechanical mechanism to transfer the rotational motion of the frontal part into the linear motion of the middle part. Using this original mechanism, the linearly moving part at the middle of the capsule robot generates a supportive driving force. The improved mobility is evaluated in experiments. The developed capsule robot employing multiple locomotion mechanisms moves 44% faster than the spiral motion-based capsule robot. The developed magnetic mechanical mechanism and the mobile robotic platform could be used for pipe inspection robots or medical robots. 相似文献
38.
An investigation into vehicle rollover prevention by coordinated control of active anti-roll bar and electronic stability program 总被引:1,自引:0,他引:1
Seongjin Yim Kwangki Jeon Kyongsu Yi 《International Journal of Control, Automation and Systems》2012,10(2):275-287
This paper presents a method for designing a controller that uses an active anti-roll bar (AARB) and an electronic stability program (ESP) for rollover prevention. ESP with longitudinal speed control (LSC) can carry out active braking to reduce vehicle speed and lateral acceleration to prevent a rollover. To enhance the rollover prevention capability of the ESP, an AARB is adopted. The controller for the AARB was designed based on linear quadratic (LQ) static output feedback (SOF) control methodology, which attenuates the effect of lateral acceleration on the roll angle and roll rate by control of the suspension stroke and the tire deflection of the vehicle. Although this AARB significantly increases ride comfort and rollover prevention, it has a drawback — the vehicle loses its maneuverability. Therefore, the ESP with LSC is used to overcome this drawback. Simulations showed that the proposed method was effective in preventing a rollover. 相似文献
39.
In this paper, we define Proteo as a class of three-dimensional (3D) metamorphic robotic system capable of approximating arbitrary 3D shapes by utilizing repeated modules. Each Proteo module contains embedded sensors, actuators and a controller, and each resides in a 3D grid space. A module can move itself to one of its open neighbor sites under certain motion constraints. Distributed control for the self-reconfiguration of such robots is an interesting and challenging problem. We present a class of distributed control algorithms for the reconfiguration of Proteo robots based on the goal-ordering mechanism. Performance results are shown for experiments of these algorithms in a simulation environment, and the properties of these algorithms are analyzed. 相似文献
40.