The Experts below are selected from a list of 5001 Experts worldwide ranked by ideXlab platform
Zhai Hongxiang - One of the best experts on this subject based on the ideXlab platform.
-
the effect of whisker orientation in sic whisker reinforced si3n4 ceramic matrix composites
Journal of The European Ceramic Society, 1999Co-Authors: Wang Changan, Huang Yong, Zhai HongxiangAbstract:Abstract Si 3 N 4 ceramic matrix composites reinforced by nearly unidirectionally aligned SiC whiskers have been prepared by extrusion and hot pressing. Unlike the case in traditional Si 3 N 4 ceramic matrix composites reinforced by random SiC whiskers, the mechanical properties of the composites exhibit a significant dependence on whisker orientation. In the direction of whisker alignment for SiC(w)/Si 3 N 4 composites, increments in bending strength and fracture toughness of 200 MPa and 3 MPa·m 1/2 are obtained respectively, compared to the values in the direction perpendicular to whisker alignment. Based on microscopic fractographic observation and micromechanics analyses, the effects of whisker orientation on toughening mechanisms are discussed. The results indicate that the whisker orientation, θ , is a decisive factor for the essential toughening mechanisms of whiskers. Only in the case of small θ and weak interface can whisker pullout occur, and whisker has maximum toughening effect. The results show that effects of whisker strengthening and toughening can be improved simultaneously through whisker oriented alignment. ©
John F Disterhoft - One of the best experts on this subject based on the ideXlab platform.
-
a novel method for precisely timed stimulation of mouse whiskers in a freely moving preparation application for delivery of the conditioned stimulus in trace eyeblink conditioning
Journal of Neuroscience Methods, 2009Co-Authors: Roberto Galvez, Craig Weiss, Sabrina Cua, John F DisterhoftAbstract:The somatosensory whisker pathway has been a useful system for increasing our understanding of experience-induced plasticity. However, precisely timed whisker activation in the awake freely moving mouse has been very difficult. This manuscript describes a method for construction of a whisker stimulator that can be attached to a freely moving mouse. The stimulator was used to activate the whiskers in a time-sensitive forebrain-dependent task, trace eyeblink conditioning. After repeatedly pairing whisker stimulation with delivery of a mild periorbital shock following a stimulus-free trace interval, trace-conditioned mice were able to learn the association. This study demonstrates the potential for using the whisker stimulator in time-sensitive behavioral tasks, such as trace eyeblink conditioning, thus enhancing our ability to examine experience-induced neuronal plasticity in the somatosensory whisker pathway in awake behaving rodents.
-
cortical barrel lesions impair whisker cs trace eyeblink conditioning
Learning & Memory, 2007Co-Authors: Roberto Galvez, Aldis P Weible, John F DisterhoftAbstract:Whisker deflection is an effective conditioned stimulus (CS) for trace eyeblink conditioning that has been shown to induce a learning-specific expansion of whisker-related cortical barrels, suggesting that memory storage for an aspect of the trace association resides in barrel cortex. To examine the role of the barrel cortex in acquisition and retrieval of trace eyeblink associations, the barrel cortex was lesioned either prior to (acquisition group) or following (retention group) trace conditioning. The acquisition lesion group was unable to acquire the trace conditioned response, suggesting that the whisker barrel cortex is vital for learning trace eyeblink conditioning with whisker deflection as the CS. The retention lesion group exhibited a significant reduction in expression of the previously acquired conditioned response, suggesting that an aspect of the trace association may reside in barrel cortex. These results demonstrate that the barrel cortex is important for both acquisition and retention of whisker trace eyeblink conditioning. Furthermore, these results, along with prior anatomical whisker barrel analyses suggest that the barrel cortex is a site for long-term storage of whisker trace eyeblink associations.
Qingchang Meng - One of the best experts on this subject based on the ideXlab platform.
-
experimental and numerical studies of the effect of whisker misalignment on the hot compressive deformation behavior of the metal matrix composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: L Geng, Qingchang MengAbstract:Abstract The combined experimental and numerical approaches are utilized to investigate the effects of the whisker misalignment and rotation on the stress–strain response of discontinuous SiC whisker reinforced aluminum matrix composites during the hot compressive deformation at 300 °C. It is found from the numerical results that the whisker orientation has significant effects on the stress and rotation of whiskers, but little influences on the flow stress and work hardening of the matrix. Both numerical and experimental results indicate that the whisker misalignment and rotation play an important role in hot deformation behavior of the composites. During the hot compressive deformation, the composites with whisker misalignment angles less than 30° exhibit strain-softening behavior due to the whisker rotation or breakage. However, the composites with whisker orientation angles more than 45° show work hardening phenomenon due to the matrix work hardening. The predicted stress–strain behavior of the composites is in qualitative agreement with the experiment results.
Wang Changan - One of the best experts on this subject based on the ideXlab platform.
-
the effect of whisker orientation in sic whisker reinforced si3n4 ceramic matrix composites
Journal of The European Ceramic Society, 1999Co-Authors: Wang Changan, Huang Yong, Zhai HongxiangAbstract:Abstract Si 3 N 4 ceramic matrix composites reinforced by nearly unidirectionally aligned SiC whiskers have been prepared by extrusion and hot pressing. Unlike the case in traditional Si 3 N 4 ceramic matrix composites reinforced by random SiC whiskers, the mechanical properties of the composites exhibit a significant dependence on whisker orientation. In the direction of whisker alignment for SiC(w)/Si 3 N 4 composites, increments in bending strength and fracture toughness of 200 MPa and 3 MPa·m 1/2 are obtained respectively, compared to the values in the direction perpendicular to whisker alignment. Based on microscopic fractographic observation and micromechanics analyses, the effects of whisker orientation on toughening mechanisms are discussed. The results indicate that the whisker orientation, θ , is a decisive factor for the essential toughening mechanisms of whiskers. Only in the case of small θ and weak interface can whisker pullout occur, and whisker has maximum toughening effect. The results show that effects of whisker strengthening and toughening can be improved simultaneously through whisker oriented alignment. ©
Meng Liu - One of the best experts on this subject based on the ideXlab platform.
-
effect of humidity on tin whisker growth from sn3nd intermetallic compound
Journal of Materials Research, 2012Co-Authors: Aiping Xian, Meng LiuAbstract:The spontaneous whisker growth phenomenon was investigated by exposing Sn3Nd intermetallic compound (IMC) to different environments. In a humid environment, tin whiskers grew rapidly; the incubation time for whisker formation was only 0.75 h. However, no whiskers were formed when Sn3Nd IMC was exposed to dry argon for 33 days or dry oxygen (DO) for 7 days. In situ observation of whisker growth during room ambient (RA) exposure gave an average whisker growth rate of the Sn3Nd IMC of about 11 angstrom/s, which are 2-3 orders of magnitude faster than that previously reported for tin plating. Following whisker growth, a new hydroxide compound, Nd (OH)(3), was found to have formed on the Sn3Nd. The results show that the presence of humidity in the exposure environment is necessary for whisker growth from Sn3Nd. Finally, the driving force for whisker growth is also discussed.
-
observations of continuous tin whisker growth in ndsn 3 intermetallic compound
Journal of Materials Research, 2009Co-Authors: Aiping Xian, Meng LiuAbstract:In situ observation of tin whisker growth in NdSn(3) compound was carried out by using an optical microscope (OM) and scanning electron microscopy (SEM). The growth rate of Sn-whisker from NdSn(3) is shown to be rapid (approximately 8-15 A/s) during exposure to room ambience, and it is accompanied by formation of a new compound, Nd(OH)(3), as was confirmed by x-ray diffraction. This reaction between the Sn-RE compound and trace water in room ambience has significant influence on whisker growth. There is an electron irradiation effect on whisker growth; that is, whiskers stopped growing after being observed in SEM. Therefore, it is suggested that OM be used rather than SEM to observe the continuous whisker growth. In discussion, the driving force per Sn atom for whisker growth is estimated as 1 x 10(14) N in accordance with the whisker growth rate, and its apparent force originates from a chemical potential gradient between the released Sri atoms and the whisker.
