Absfracr-In many sensor-based path-planning algorithms, the worst path length has been theoretically evaluated, but the average path length Will not be theoretically and experimentally evaluated at all. In general, shorting average path length is worth much than shorting worst path length in the practical use. Therefore, we propose a new sensor-based path-planning algorithm whose path length is exactly shorten on the average. The algorithm always expands the best crack of a spanned graph from an initial position. AIL cracks mean all tips or routes traced from hit and/or leave points and also all neighbors of hit and/or leave points not to trace. The evaluation and expansion work by A' in the spanned graph. By selection of the hest node, a mobile robot frequently reverses its direction following an uncertain obstacle. For this w o n , the robot frequently passes through a shorter interval around an unknown obstacle thme times or more. As a result, the worst path length cannot be bounded as any small value. However, a total driving distance is completely saved by following a short boundary three times or more, which is raster than following a long boundary two times. In this paper, we ascertain the superlority of our algorithm experimentally by a huge number of unknown environmenls. I. lNTnouucnoNIn the last'two decades, many researchers have proposed sensor-based path-planning algorithms while focusing on worst and average path lengths. Concerning to the worst path length, Sankaranarayanan classified and evaluated the lowet bounds of two types of sensor-based path-planning algorithms. In the former type, a robot always goes round an obstacle as long as the robot encounters the obstacle. The lowe1 bound is denoted by D t 1.5ZiPi (D: the Euclidean distance between initial and target positions, Pi: the perimeter of an i-th encountered obstacle) [I]. On the other hand, in the latter type, a robot does not always go round an obstacle even though the robot meets the obstacle. The lower hound is denoted by D t 2&Pi [I]. As a result, the classic algorithm Bug1 proposed by Lumelsky is the best in the former type [21, and the algorithms A f g l and Alg2 proposed by Sankaranarayanan are the hest in the latter type [3], [4]. Recently, we propose the algorithms Rev1 and Rev2 whose worst path length is bounded by D t Z i p i , and whose average path length is shorter than that of Algl and Alg2 [51,[61.As contrasted with this, no researcher has evaluated the average path length in a general uncertain environment. As the unique exception, if each obstacle has simple shape such as circle in a general uncertain environment, we proposed a near-optimal sensor-based path-planning algorithm Simple and calculated a small competitive ratio between lengths of the optimal path and a selected path as 1.58 [7]. This requests a strong assumption of environment shape. In general, shorting average path length is more worth than shorting worst path length in the practical use. In addition, an algorithm whose worst path length is the shortest qui...
Absnoet-In this paper, we compare two major structures of MSD (Mass-Spring-Damper) particle models. One is the lattice (hexahedral) struchm, and the other iS the truss (tetrahedral) structure. They (especially, the truss structure) hare been frequently used for represenling elastic andlor visco-elaslic object. The MSD model eBciently calculates shapc deformation of the above materials. In addition, in order lo maintain shape precision of each deformation, we carefully calibrate coefficienls of damper and spring of Voigt part and a cocfficicnt of damper of thc other part in thc basic MSD element under many surface points capturing a real rheologic object A genetic algorithm is used for probabilistic calibration. Aner the comparisnn, we get the following properlies:(1) The lattice structure has too many elements for calculating force propagation. Therefore, it precisely leads shape deformation with the help of the local (feed-forward) w l m e constant condition.(2) The truss structure does not have enough elements for propagating internal forces. Therefore, in order lo keep B reasonable volume by expanding ils virtual rheology object, we oced the global (feed-back) volume constant condition.(3) The global condition is time consuming, but c m directly control the total volume of virtual rheology object. On the other hand, the local one is quick, but direcUy expands only a part (voxel) of the virtual object. Therefore, the volume and shape in the lattice structure with the local condition are better than those in the truss slmcture including the global one.(4) The number of MSD elemenls in the lattice structure is about two times larger than that in the truss one. Therefore, the former calculation is about two times slower than the latter one. As contrasted with this, the global volume constant condition is strictly two times or more slower lhan the local one. As a result, calculation time of the laltiec struchm with the local condition is smaller than that of the truss structure wilh the global one.ln conclusion, the lattice slmctuie with the local volume constant condition is the best concerning Lo calculation cost and shape prerision.
Background Spinal intradural (subdural and subarachnoid) hematoma following percutaneous kyphoplasty is an extremely rare complication. In this report, we describe a case of subarachnoid hemorrhage with delayed paralysis after kyphoplasty and review the literature on similar cases to describe the complications of kyphoplasty and vertebroplasty (VP). Case Description An 80-year-old man underwent percutaneous kyphoplasty at a local hospital an osteoporotic vertebral fracture (OVF) at the T12 and L1 level. On the second day after kyphoplasty for T12 OVF, he developed paralysis of the lower limbs. At his initial visit to our clinic, he had a complete loss of sensation below T11 and complete paralysis of both lower extremities. Thoracolumbar magnetic resonance imaging revealed an intradural hematoma on the ventral side of the spinal cord, in the spinal canal from T5 to T12, compressing the spinal cord. Thoracolumbar computed tomography showed a fracture line in the medial cortex of the right pedicle at T12 and a tract from the spinal canal to the vertebral body. An emergency posterior decompression from T11 to L1 was performed. A small hole was found on the right side of the pedicle at T12, and tear of the nerve and subarachnoid hematoma were observed in the vicinity of the T11 nerve root. The subarachnoid hematomas were removed. Postoperatively, the neurological symptoms improved rapidly. Eventually, he was able to walk and was transferred for rehabilitation. Conclusions Percutaneous surgery through the pedicle might cause hematoma and bone cement leakage into the spinal canal. This can be a serious complication: hence prevention is important.
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