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201.
For bulk piezoelectric ceramics plates, the fundamental thickness-stretch (TSt) waves are always coupled to the in-plane extension waves and the symmetric thickness-shear waves. The occurrence of these spurious modes in bulk piezoelectric ceramics plates is undesirable as it may interfere with the operation of transducers. 1–3 piezoelectric composites are promising candidates to suppress the spurious modes mentioned above. However, theoretical modelling of multiphase ceramic composite objects is very complex. In this study, a simple analytical TSt vibration model is constructed from three-dimensional equations of linear piezoelectricity. The mechanical damping is considered in the model by introducing a complex elastic constant. The performance of 1–3 piezoelectric composites is analysed and the electrical impedance results from theoretical and experimental analysis are compared. The results show that there is excellent agreement between the experimental electrical impedance and that obtained by the theoretical TSt vibration analysis. This indicates that 1–3 piezoelectric composites can be operated in a nearly pure TSt vibration mode near the fundamental resonance. The analytical model we present is valid for analysing 1–3 piezoelectric composites plates with large aspect ratios quickly and efficiently. 相似文献
202.
Dafan Du Jiang Wang Yves Fautrelle Zhongming Ren Rene Moreau 《Philosophical Magazine Letters》2015,95(8):425-432
The application of a high magnetic field is capable of inducing the formation of aligned equiaxed grains in alloys during directional solidification. The alignment and refinement of the grains is enhanced as the magnetic field intensity increases. The thermoelectric power difference at the liquid/solid interface in four alloys has been measured in situ during directional solidification and it is concluded that the formation of aligned equiaxed grains in a magnetic field should be attributed to the combined action of a thermoelectric magnetic force and a magnetization force. 相似文献
203.
The directional solidification process of ternary Ag42.4Cu21.6Sb36 eutectic alloy within a wide growth rate range from 2 to 60 μm/s was accomplished at a constant temperature gradient of 50 K/cm. As growth rate increases, the ternary (θ(Cu2Sb) + ε(Ag3Sb) + Sb) eutectic morphology evolves from “lamellar (θ + ε) plus fibrous (Sb)” structure into “(θ + Sb) fibres in continuous ε matrix” structure. The θ and (Sb) phase spacings decrease with the increase of growth rate according to power functions with exponent values of 0.55 and 0.56, respectively. It is also found that the microhardness of directionally solidified Ag42.4Cu21.6Sb36 alloy samples is enhanced with the increase of growth rate, and the decrease of θ and (Sb) phase spacings. 相似文献
204.
205.
This special issue of Memory brings together research from around the globe, from Japanese, Chinese and East Indian cultures, to American and European societies, to the Caribbean, to Turkey and to Australia and New Zealand, which examines how and why people, from childhood to old age, remember the personal past in daily life. This journey highlights the important role of the cultural context in shaping the functional usages of autobiographical memory. We illuminate six major contributions of cross-cultural research to a broader and deeper understanding of the functions of autobiographical memory, and call attention to the filed that memory research must “go global.” 相似文献
206.
This study investigated explicit knowledge of autobiographical memory functions using a newly developed questionnaire. European and Asian American adults (N = 57) and school-aged children (N = 68) indicated their agreement with 13 statements about why people think about and share memories pertaining to four broad functions—self, social, directive and emotion regulation. Children were interviewed for personal memories concurrently with the memory function knowledge assessment and again 3 months later. It was found that adults agreed to the self, social and directive purposes of memory to a greater extent than did children, whereas European American children agreed to the emotion regulation purposes of memory to a greater extent than did European American adults. Furthermore, European American children endorsed more self and emotion regulation functions than did Asian American children, whereas Asian American adults endorsed more directive functions than did European American adults. Children's endorsement of memory functions, particularly social functions, was associated with more detailed and personally meaningful memories. These findings are informative for the understanding of developmental and cultural influences on memory function knowledge and of the relation of such knowledge to autobiographical memory development. 相似文献
207.
208.
Ameneh Shahaeian Julie D. Henry Maryam Razmjoee Ali Teymoori Cen Wang 《Developmental science》2015,18(5):671-685
Previous research has consistently indicated that theory of mind (ToM) is associated with executive control in the preschool years. However, interpretation of this literature is limited by the fact that most studies have focused exclusively on urbanized Western cultural samples. Consequently, it is not clear whether the association between ToM and executive control reflects the specific features of this particular cohort or instead reflects a universal pattern. The present study provides the first empirical assessment of these two constructs in three diverse groups of Iranian children. Participants were 142 preschoolers (4–5 years old) from high–socioeconomic status (SES) urban (n = 33), low–SES urban (n = 37) and rural villages (n = 77). The results show that there is a robust association between ToM and executive control in all three groups, and that executive control contributes significant unique variance to ToM understanding, even after controlling for a range of variables that have been proposed as potential confounders of this relationship. However, although the three groups were equated in ToM, significant differences in executive control were evident. Moreover, cluster analysis identified three distinct clusters that were relatively homogeneous with respect to executive control and SES. One of these clusters was characterized by both low SES and low executive functioning, and showed little evidence of ToM understanding. Taken together, these findings provide possibly the clearest evidence to date that the association between ToM and executive control is not dependent on children's previous experiences on the tasks, or their family and cultural background. A video abstract of this article can be viewed at https://www.youtube.com/watch?v=dxh_-3gCB8o 相似文献
209.
A unified fielder theory is presented that explains how humans navigate to intercept targets that approach from either above
or below the horizon. Despite vastly different physical forces affecting airborne and ground-based moving targets, a common
set of invariant perception-action principles appears to guide pursuers. When intercepting airborne projectiles, fielders
keep the target image rising at a constant optical speed in a vertical image plane and moving in a constant optical direction
in an image plane that remains perpendicular to gaze direction. We confirm that fielders use the same strategies to intercept
grounders. Fielders maintained a cotangent of gaze angle that decreases linearly with time (accounting for 98.7% of variance
in ball speed) and a linear optical trajectory along an image plane that remains perpendicular to gaze direction (accounting
for 98.2% of variance in ball position). The universality of maintaining optical speed and direction for both airborne and
ground-based targets supports the theory that these mechanisms are domain independent. 相似文献
210.
Spatial updating relies on an egocentric representation of space: Effects of the number of objects 总被引:1,自引:0,他引:1
Wang RF Crowell JA Simons DJ Irwin DE Kramer AF Ambinder MS Thomas LE Gosney JL Levinthal BR Hsieh BB 《Psychonomic bulletin & review》2006,13(2):281-286
Models of spatial updating attempt to explain how representations of spatial relationships between the actor and objects in
the environment change as the actor moves. In allocentric models, object locations are encoded in an external reference frame,
and only the actor’s position and orientation in that reference frame need to be updated. Thus, spatial updating should be
independent of the number of objects in the environment (set size). In egocentric updating models, object locations are encoded
relative to the actor, so the location of each object relative to the actor must be updated as the actor moves. Thus, spatial
updating efficiency should depend on set size. We examined which model better accounts for human spatial updating by having
people reconstruct the locations of varying numbers of virtual objects either from the original study position or from a changed
viewing position. In consistency with the egocentric updating model, object localization following a viewpoint change was
affected by the number of objects in the environment. 相似文献