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1.
Torsion of noncircular beams results in warping of each cross section. When noncircular cross sections are constrained to remain plane, the resulting shear stress distribution is different from what Saint Venant torsion (with warping) would predict. This has practical implications to the stress analysis of plated long bones subjected to torsional loadings. Analyses in which warping is not allowed predict incorrect stress fields in the plate and bone and overpredict the amount of stress shielding associated with fracture plate fixation. 相似文献
2.
The capacity for short-term adaptation is a well-established property of the horizontal (H) and vertical (V) components of saccades. It allows these directional components, which clearly serve the goal of foveation, to maintain their precision even under changing circumstances. Torsional (T) saccade components, on the other hand, which deal with the orientation of the target on the fovea, have hardly been investigated in adaptation experiments. They appear to be severely restricted by Listing's law during fixations and saccades. The main purpose of Listing's law is far from obvious but could be visual or oculomotor. Better knowledge of the adaptive capacity of the saccadic system in the torsional direction could throw new light on the functional significance of this interesting neural strategy. To study short-term plasticity in the torsional components of saccades, binocular 3D-eye positions were measured, using magnetic search foils. Five normal human subjects were instructed to make uni-directional refixation saccades, while they viewed a large visual scene. To induce a change in the torsional component, the complete stimulus was rapidly rotated during these saccades. We thoroughly investigated the torsional responses of the saccadic system, to see if any short-term adaptive response in torsional direction was induced, in which case the notion of a visual purpose for Listing's law would be strengthened. In none of our experiments, however, did we find any clear adaptive response in torsional direction. To further investigate the reliability of this result and to ascertain that our experimental conditions allowed classical gain adaptation, we also did experiments designed to achieve a combination of torsional adaptation and classic gain shortening in one of the directional components. While gain adaptation was very obvious, none of the experiments provided evidence for a short-term effect in torsion. We conclude that our experiments do not support a purely visual basis for Listing's law. 相似文献
3.
I. P. Howard J. E. Zacher 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1991,85(2):445-450
Summary By the use of scleral search coils a continuous record of human cyclovergence was obtained while two identical 80° textured patterns, presented dichoptically, oscillated in the frontal plane in counterphase through 1, 3 and 6° of cyclorotation at frequencies between 0.05 and 2 Hz. The amplitude and gain of the response decreased exponentially with increasing stimulus frequency. As stimulus amplitude increased, response amplitude also increased but gain was highest for low-amplitude cyclorotations. For an amplitude of 1° and a frequency of 0.05 Hz the gain reached 0.87 for two subjects. The phase lag increased from a few degrees at a frequency of 0.05 Hz to over 100° at a frequency of 2 Hz. These results suggest that cyclovergence is designed to correct for small, slow drifts in the stereoscopic alignment of the images in the two eyes. Although the disparity in the textured display was not interpreted as slant, it provided a strong stimulus for cyclovergence. The cyclovergence caused a transfer of cyclodisparity into a superimposed vertical line, which was then perceived as slanting in depth. 相似文献
4.
Human ocular counterroll: assessment of static and dynamic properties from electromagnetic scleral coil recordings 总被引:1,自引:0,他引:1
H. Collewijn J. Van der Steen L. Ferman T. C. Jansen 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1985,59(1):185-196
Summary Static and dynamic components of ocular counterroll as well as cyclorotatory optokinetic nystagmus were measured with a scleral search coil technique. Static counterroll compensated for about 10% of head roll when the head was tilted to steady positions up to 20 deg from the upright position. The dynamic component of counterroll, which occurs only while the head is moving, is much larger. It consists of smooth compensatory cyclorotation opposite to the head rotation, interrupted frequently by saccades moving in the same direction as the head. During voluntary sinusoidal head roll, cyclorotation compensated from 40% to more than 70% of the head motion. In the range 0.16 to 1.33 Hz, gain increased with frequency and with the amount of visual information. The lowest values were found in darkness. The gain increased in the presence of a visual fixation point and a further rise was induced by a structured visual pattern. Resetting saccades were made more frequently in the dark than in the light. These saccades were somewhat slower than typical horizontal saccades. Cyclorotatory optokinetic nystagmus could be induced by a patterned disk rotating around the visual axis. It was highly variable even within a same subject and had in general a very low gain (mean value about 0.03 for stimulus velocities up to 30 deg/s). It is concluded that cyclorotational slip velocity on the retina is considerably reduced by counterroll during roll of the head, although the residual cyclorotation after the head has reached a steady position is very small. 相似文献
5.
模拟股骨置入人工关节扭转与应力松弛蠕变的实验研究 总被引:1,自引:0,他引:1
研究了在相同扭矩作用下,正常组股骨和以生物学和骨水泥固定置入人工关节组股骨标本扭转角度,还对正常股骨、生物学固定股骨和骨水泥固定股骨进行应力松弛、蠕变实验,为临床提供生物力学参数。以电子万能试验机对正常对照组、股骨置入人工关节骨水泥固定组、股骨置入人工关节生物学固定组标本进行扭转和粘弹性实验研究。得出了各组标本在相同扭矩下的扭转角度及悬臂弯曲状态下,正常组和置入人工关节组标本应力松弛、蠕变数据和曲线。对实验数据进行归一化处理,得出了正常组和置入人工关节组标本的归一化应力松弛函数,归一化蠕变函数及曲线。表明:骨水泥固定组扭转角比生物学固定组小,说明骨水泥固定有较好的稳定性,其应力松弛、蠕变量丢失小。骨水泥固定组较生物学固定组3600s应力松弛、蠕变量大。 相似文献
6.
Protection of the solitary testis 总被引:1,自引:0,他引:1
In 15 negative explorations for unilateral cryptorchidism, inspection of the contralateral scrotum revealed a "bell-clapper" deformity in 13 patients. Since the descent of the testis is influenced by the gubernaculum and gubernacular abnormalities are usually bilateral, the data suggest that an inadequate gubernaculum is associated with most instances of antenatal and postnatal torsion. Unilateral absence of the testis is a form of this syndrome; congenital monorchidism is probably due to antenatal torsion rather than hypoplasia or agenesis. When monorchidism is confirmed at operation, exploration and suture fixation of the contralateral testis at the same procedure is recommended to protect the solitary testis from future torsion. 相似文献
7.
目的 提高睾丸扭转的诊治水平。方法 回顾性分析总结16例睾丸扭转的临床资料。结果 16例均经彩色多谱勒血流成像(Color Doppler ultrasonics flow image,CDFI)确诊为睾丸扭转,2例经手法复位,5例经手术复位固定,9例行睾丸切除加对侧睾丸固定。11例获0.5~4.5年随访,手法复位者1例再次发生扭转,经手术复位治愈。结论 CDFI是诊断急性睾丸扭转的可靠方法,早期诊断、及时手术探查是提高睾丸存活率的关键,术中应同时固定对侧睾丸。 相似文献
8.
目的比较长型PHILOS接骨板(Synthes公司,瑞士)扭转成螺旋形前后的生物力学特性,为临床治疗肱骨中上段骨折提供生物力学依据。方法 12例Synbone人工骨(SYNBONE公司,瑞士)的右侧肱骨平均分为两组,对照组(n=6)采用10孔的长型PHILOS接骨板固定,实验组(n=6)采用相同的接骨板扭转成螺旋形后固定。肱骨中上段骨折造模后,利用万能力学试验机分别检测并比较两组接骨板固定后的整体构件在轴向拉伸和压缩、同向和反向扭转、前后及内外向三点弯曲6种加载方式下的生物力学特性。结果在100~500 N拉伸和压缩载荷下,实验组骨折断端位移分别较对照组增加约95%和58%;在0.6~3 N·m反向扭矩下,实验组扭转角度始终明显小于对照组,减少幅度达到55%~64%;在0.6~3 N·m的同向扭矩和1.5~7.5 N·m的前后向弯矩下,实验组的扭转角度和桡度均大于对照组,差异有显著性意义(P0.05);当内外向弯矩为1.5、3 N·m时,实验组与对照组的桡度差别无显著性意义(P0.05),而内外向弯矩为4.5、6、7.5 N·m时,实验组的桡度较对照组小20%~30%。实验组与对照组构件相比,拉伸和压缩刚度分别低49%和36%,同向和反向扭转刚度分别低19%和高150%,内外向和前后向弯曲刚度分别高18%和低70%,差异均有显著性意义(P0.05)。结论长型PHILOS接骨板扭转成螺旋形后固定肱骨中上段骨折的总体力学性能有所改善,可以满足临床对该类骨折的手术固定和术后康复需要。结合微创手术的优势,该技术有望在临床得到广泛应用。 相似文献
9.
Mohsen Rouzrokh Alireza Mirshemirani Ahmad Khaleghnejad-Tabari 《Iranian journal of pediatrics.》2015,25(4)
Background:
Testicular torsion (TT), or twisting of the testicle resulting in a strangulation of the blood supply, occurs in men whose tissue surrounding the testicle is not well attached to the scrotum. It is important to emphasize that testicular torsion is a medical emergency.Objectives:
The aim of this study is to evaluate the second look exploration and outcomes in TT.Patients and Methods:
Seventy boys out of 124 patients underwent early exploration and 48 hours later second look exploration due to TT. All patients were checked with preoperative color-doppler ultrasonography (CDU) and intraoperative bleeding test. Data included age at admission, side of pathology, relation of TT with season of year, duration of preoperative history, degree of testicular torsion, CDU findings, and degree of bleeding; results of second look exploration, follow-up, and outcomes were analyzed.Results:
Totally 70 patients were included in this study within five years, of which mean age was 28.6 ± 32.9 months (range 1 to 144), 48% of our patients had nausea and vomiting. Preoperative CDU showed absent/weak flow in 50 (71%) cases. Winter showed most frequently (44%) referred cases of testicular torsion. Orchidopexy was performed in 44 (63%) and orchidectomy in 26 (37%) cases after second look exploration. Mean follow-up duration was 3.1 ± 1.4 years. 4 (9%) cases in orchidopexy group developed testicular atrophy during follow-up, all four cases had a history of longer than 12 hours and grade II testicular bleeding test intra-operatively. Other orchidopexy patients salvaged. 26 patients, who were in grade III, underwent orchidectomy in second look exploration.Conclusions:
TT requires emergency attention. The ischemia time of the testis is traditionally after 6 hours, and imaging or other diagnostic modality should not be a cause of delay. Early surgical exploration is modality of choice, and second look exploration after 48 hours can be more effective and salvageable in these patients. 相似文献10.
Arno Bisschop Jaap H. van Dieën Idsart Kingma Albert J. van der Veen Timothy U. Jiya Margriet G. Mullender Cornelis P. L. Paul Marinus de Kleuver Barend J. van Royen 《European spine journal》2013,22(8):1785-1793