共查询到20条相似文献，搜索用时 40 毫秒
1.
Oury F Murakami Y Renaud JS Pasqualetti M Charnay P Ren SY Rijli FM 《Science (New York, N.Y.)》2006,313(5792):1408-1413
In the mouse trigeminal pathway, sensory inputs from distinct facial structures, such as whiskers or lower jaw and lip, are topographically mapped onto the somatosensory cortex through relay stations in the thalamus and hindbrain. In the developing hindbrain, the mechanisms generating such maps remain elusive. We found that in the principal sensory nucleus, the whisker-related map is contributed by rhombomere 3-derived neurons, whereas the rhombomere 2-derived progeny supply the lower jaw and lip representation. Moreover, early Hoxa2 expression in neuroepithelium prevents the trigeminal nerve from ectopically projecting to the cerebellum, whereas late expression in the principal sensory nucleus promotes selective arborization of whisker-related afferents and topographic connectivity to the thalamus. Hoxa2 inactivation further results in the absence of whisker-related maps in the postnatal brain. Thus, Hoxa2- and rhombomere 3-dependent cues determine the whisker area map and are required for the assembly of the whisker-to-barrel somatosensory circuit. 相似文献
2.
应用简支梁振动理论、推导出由冲南喷激振作用下测得的 支梁桥的自振频率f0以此得出各主梁在外荷载作用下的跨中挠度的计算方法，并对两座配筋砼简支梁桥的动载试验数据进行了实例计算，将计算结果，与采静载试验得得的跨中挠度进行了比较，二者符合情况良好，这表明采用既经济又简便的动载测试方法来确定等截面简支梁刚度是可行的。 相似文献
3.
利用等效夹杂理论及能量释放率导出了金属基复合材料短裂纹疲劳扩展速率，公式中考虑了晶须及裂纹前端塑性区对裂纹的影响，并给出了等效裂纹长度公式。将理论结果同实验结果进行了比较，吻合得较好；分析了短裂纹扩展规律，指出晶须对裂纹扩展的作用及在裂纹越过晶须一段距离后，可以认为晶须已经失去增强作用，此时相当于无晶须的情形。 相似文献
4.
Graphite whiskers (GWs), an allotrope of carbon that has been proposed to occur in space, have been discovered in three CV-type carbonaceous chondrites via Raman imaging and electron microscopy. The GWs are associated with high-temperature calcium-aluminum inclusion (CAI) rims and interiors, with the rim of a dark inclusion, and within an inclusion inside an unusual chondrule that bears mineralogy and texture indicative of high-temperature processing. Current understanding of CAI formation places their condensation, and that of associated GWs, relatively close to the Sun and early in the condensation sequence of protoplanetary disk materials. If this is the case, then it is a possibility that GWs are expelled from any young solar system early in its history, thus populating interstellar space with diffuse GWs. Graphite whiskers have been postulated to play a role in the near-infrared (near-IR) dimming of type Ia supernovae, as well as in the thermalization of both the cosmic IR and microwave background and in galactic center dimming between 3 and 9 micrometers. Our observations, along with the further possibility that GWs could be manufactured during supernovae, suggest that GWs may have substantial effects in observational astronomy. 相似文献
5.
李明瑞 《中国农业大学学报》1996,1(2):17-24
统一地作出了梁板壳结构的运动学分析，第一次指出了有限转动矩阵的精确使用方法，从而建立起全部的完整有限变形理论，并推导出板壳有限变形的精确方程，使可替代von－Karman薄板大挠度方程。 相似文献
6.
Matyas F Sreenivasan V Marbach F Wacongne C Barsy B Mateo C Aronoff R Petersen CC 《Science (New York, N.Y.)》2010,330(6008):1240-1243
Classical studies of mammalian movement control define a prominent role for the primary motor cortex. Investigating the mouse whisker system, we found an additional and equally direct pathway for cortical motor control driven by the primary somatosensory cortex. Whereas activity in primary motor cortex directly evokes exploratory whisker protraction, primary somatosensory cortex directly drives whisker retraction, providing a rapid negative feedback signal for sensorimotor integration. Motor control by sensory cortex suggests the need to reevaluate the functional organization of cortical maps. 相似文献
7.
In the polymerization of alpha-olefins with heterogeneous Ziegler-Natta catalysts, the polymer is formed directly as long fibrillar units with folder chains. It is proposed that the fibrils are formed by the crystallization of polymer chains growing from the active sites on the catalyst surface, a process which is likened to root growth in whiskers. 相似文献
8.
Static and dynamic mechanical deflections were electrically induced in cantilevered, multiwalled carbon nanotubes in a transmission electron microscope. The nanotubes were resonantly excited at the fundamental frequency and higher harmonics as revealed by their deflected contours, which correspond closely to those determined for cantilevered elastic beams. The elastic bending modulus as a function of diameter was found to decrease sharply (from about 1 to 0.1 terapascals) with increasing diameter (from 8 to 40 nanometers), which indicates a crossover from a uniform elastic mode to an elastic mode that involves wavelike distortions in the nanotube. The quality factors of the resonances are on the order of 500. The methods developed here have been applied to a nanobalance for nanoscopic particles and also to a Kelvin probe based on nanotubes. 相似文献
9.
Krupa DJ Wiest MC Shuler MG Laubach M Nicolelis MA 《Science (New York, N.Y.)》2004,304(5679):1989-1992
Ensemble neuronal activity was recorded in each layer of the whisker area of the primary somatosensory cortex (SI) while rats performed a whisker-dependent tactile discrimination task. Comparison of this activity with SI activity evoked by similar passive whisker stimulation revealed fundamental differences in tactile signal processing during active and passive stimulation. Moreover, significant layer-specific functional differences in SI activity were observed during active discrimination. These differences could not be explained solely by variations in ascending thalamocortical input to SI. Instead, these results suggest that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing. 相似文献
10.
采用ANSYS程序计算了热力联合作用下圆板的轴对称跳跃规律,得到了用板中心挠度表示的跳跃过程和跳跃后临界挠度温升和临界横载温升关系。结果表明,临界挠度与温升或临界横载与温升都呈非线性递增关系。 相似文献
11.
通过对以纳米碳管为媒介生长的一未知纳米晶须进行的系列倾电子衍射实验,测定了该晶须为正交结构的Ｓｉ２Ｎ２Ｏ;针对常用的系列倾电子衍射实验的倾角计算公式,讨论了带轴间夹角与膜面法线转角的差异,并推导了其精确表达式。 相似文献
12.
[目的]研究全须西洋参的干制加工方法。[方法]研究洗参方法、灭酶方法、干制温度、整形理须、保护参须等工序对全须西洋参品质的影响,并对工艺参数进行优化试验,得出最佳方案。[结果]全须西洋参干制要选择优质原料、清洗泥沙、保护参须,用沸水烫或蒸汽蒸至参体变软,干制中期温度保持在33~35℃最适宜,脱水至50%左右整形理须,才能保证全须西洋参的商品价值最好。[结论]该研究为参农进行全须西洋参干制加工提供理论依据。 相似文献
13.
有/无固定墩跨越管道的内力和变形比较 总被引：9，自引：4，他引：5
考虑几何非线性,导出了有固定墩跨越管道的内力和挠度计算公式,并从中推荐了简单实用的计算式,通过比较有／无固定墩跨越管道的内力和挠度,得出结论：固定墩减小了管道的挠度、轴向拉力及当量轴向拉力,增大了轴向压力及应量轴向压力;当当量轴向力为压力／拉力时,无固定墩跨越管道的最大弯矩大于／小于有固定墩时的值;有固定墩跨越的管道嵌固端的弯矩与跨中的弯矩相比,绝对值大,无固定墩跨越管道的两者大小关系主要取决于 相似文献
14.
利用等效夹杂理论计算基体中的应力。在应变控制状态下，导出了用有效应力预报疲劳寿命的方程。从理论上展示了各组分材料对疲劳裂纹萌生寿命的影响，并用寿命曲线表示出理论结果：晶须增强金属基复合材料的疲劳性能比纯基体的高；疲劳裂纹萌生寿命曲线与宏观疲劳寿命曲线形式类似、且存在疲劳裂纹萌生极限。 相似文献
15.
A promising approach for detecting biomolecules follows their binding to immobilized probe molecules on microfabricated cantilevers; binding causes surface stresses that bend the cantilever. We measured this deflection, which is on the order of tens of nanometers, by embedding a metal-oxide semiconductor field-effect transistor (MOSFET) into the base of the cantilever and recording decreases in drain current with deflections as small as 5 nanometers. The gate region of the MOSFET responds to surface stresses and thus is embedded in silicon nitride so as to avoid direct contact with the sample solution. This approach, which offers low noise, high sensitivity, and direct readout, was used to detect specific binding events with biotin and antibodies. 相似文献
16.
Vacuum sublimation of oriented single crystals of ice at temperatures from -110 to -60 degrees Celsius was studied by electron microscopy with the freeze-etch technique. Sublimation etches the ice surface to produce pits and asperities and above -85 degrees Celsius causes extreme surface roughening. The etch pits are ascribed to surface dislocations, and the extreme roughening is ascribed to the departure from unity of the vaporization coefficient. The asperities could not be attributed to impurities; they may be related to the whiskers that others have observed at higher temperatures. 相似文献
17.
用热酚—水法提取沙门氏菌脂多糖(LPS),经pH8.0热处理后,致敏醛化的绵羊红血球,建立了一种快速检测抗沙门氏菌O抗原单克隆抗体的微量间接血凝试验。用致敏血球在96孔V型血凝板上与杂交瘤培养上清作凝集试验,数秒钟即能判定结果。本试验具有快速的特点,且有一定的敏感性。 相似文献
18.
The proposed sterility test for penicillin, which employs cysteine (in the form of its hydrochloride) rather than Clarase, has proven to be satisfactory in our laboratories. The use of cysteine is advantageous because it is a compound of known structure and is readily available at relatively small cost. Suitable samples of Clarase or bacterial penicillinases are not as reproducible and the latter require much time and effort in their preparation. Furthermore, cysteine solutions do not require filtration but may be sterilized by heat in the autoclave. 相似文献
19.
