Xiao-lei Wang

Design principles for the area density of dimple patterns

Increasing interest has been paid to surface texturing in order to improve tribological properties of sliding surfaces. Currently, the patterns of micro-dimples have attracted more attention since such closed texture cells are supposed to generate additional hydrodynamic pressure easily. It has been proven that the area density of the dimple pattern is a critical parameter for hydrodynamic pressure generation. However, the optimal values of area density obtained by theoretical models are usually different to that obtained from experiments, which show material dependence. In order to understand the design principles of the area density for mixed lubrication regime, a brief review on the studies related to the area density issue of dimple patterns is carried out; the phenomena during contacting and sliding are analyzed numerically in this paper. It is found that the stress concentration and deformation will occur on the contacting and sliding area, and influence the tribological properties of the textured surface significantly depending on the area density and material properties. These negative influences should be considered carefully during surface texture design.

Optical Reflectivity of Single Crystals of YBa2Cu3O7-δ and ErBa2Cu3O7-δ

Optical reflectivity in the ab-plane of single crystals of YBa2Cu3O7-δ and ErBa2Cu3O7-δ has been observed at room temperature in the energy region from 0.5 to 5.6 eV. The reflectivity is isotropic in the ab-plane around the Drude edge at 1.5 eV. In the low-energy region below the edge, it is explained well by the Drude formula for the free carriers with an extremely short relaxation time of about 4×10-16 s.

Maternal teaching strategies in four cultural communities Implications for early childhood teachers

This article examines maternal everyday teaching strategies in Chinese, American, Hutterite, and Native American cultural communities. It moves beyond a theoretical framework based on distancing by suggesting that effective adult teaching strategies are contextually and culturally determined. The authors urge early childhood educators to make efforts to understand the complexity of a childs home learning environment and to maximize the learning potential of every child by taking advantage of his/her funds of knowledge in early childhood education settings.

Biomimetic surface design for ultrahigh molecular weight polyethylene to improve the tribological properties

Tribological problem is a major obstacle that limits the using of ultrahigh molecular weight polyethylene (UHMWPE) in industrial applications and orthopedic surgeries. Many efforts have been made to improve the tribological properties of UHMWPE, such as promoting the structure, morphology, and mechanical properties of the polymer. Inspired by the features of articular surface, micro-scaled texture is introduced to improve the tribological properties of UHMWPE using micro-imprint lithography. Friction and wear experiments are conducted on textured and untextured specimens using ring-on-disc test apparatus under water lubrication. The experimental results demonstrate that the micro-scaled surface texture can remarkably improve the tribological properties of UHMWPE. Friction force can be effectively reduced by selecting suitable dimple parameters. Compared with an untextured UHMWPE, the textured one with optimum parameters shows a reduction in the friction coefficient as much as 66.7–85.7% on different load–speed conditions. The optimized area density of surface textured UHMWPE ranges from 22.9% to 29.9%, which is obviously higher than that of stiff materials such as metals and ceramics. The textured UHMWPE with area density 29.9%, diameter 50 µm, and depth 15 µm presents a significant effect of wear resistance. The average wear depth of textured UHMWPE is 35.5% of that of untextured one.

Variations of Maternal Support to Children's Early Literacy Development in Chinese and American Indian Families: Implications for Early Childhood Educators.

This paper presents a study that aims to help early childhood educators understand the cultural context in early language and literacy development. It examines how mothers in Chinese and American Indian families support their young children’s emergent literacy development during everyday interactions. Twenty mother-child dyads in each cultural community participated in the study. The results of the study indicate that Chinese and American Indian mothers differed greatly in the ways they supported their children in early literacy. The Chinese mothers tended to privilege print-based literacy interactions more than the American Indian mothers. The American Indian mothers tended to privilege the literacy interactions that were based on oral narratives of life and personal experiences. Moreover, the mothers in the two communities emphasized and supported different aspects of their children’s early literacy development. The Chinese mothers tended to support their children in explicit, event-specific and elaborative ways. In contrast, the American Indian mothers tended to support their children in implicit and contextual ways. This study suggests that early childhood educators must understand the specific meanings of early literacy in different cultural contexts to maximize the learning potential of every child in the early childhood education settings.ResumenEste documento presenta un estudio cuyo propósito es ayudar a los educadores de la infancia temprana a entender el contexto cultural en el desarrollo temprano del lenguaje y la lecto-escritura. Examina como las madres de familias chinas e indias americanas apoyan el desarrollo de la lecto-escritura temprana en las intracciones cotidianas. Veinte parejas madrehijo de cada comunidad cultural participaron en el estudio. Los resultados del estudio indican que las madres chinas e indias americanas difieren grandemente en la forma en que apoyan a sus hijos en la lecto-escritura temprana. Las madres chinas tendieron a privilegiar las interacciones de lecto-escritura basada en lenguaje impreso más que las madres indias americanas. Las madres indias americanas tendieron a privilegiar las interacciones de lectoescritura basadas en narrativas orales sobre experiencias de vida y personales. Además, las madres de las dos comunidades enfatizaron y apoyaron diferentes aspectos del desarrollo temprano de lecto-escritura. Las madres chinas tendieron a apoyar a sus hijos de manera explicita, especifica del evento y elaborada. En contraste, las madres indias americanas tendieron a apoyar a sus hijos de forma implícita y contextual. Este estudio sugiere que los educadores de la infancia temprana deben entender los significados especificos de la lectoescritura temprana en diferentes contextos culturales para maximizar el potencial de aprendizaje de cada niño en los escenarios educativos de la infancia temprano.RésuméCette étude vise à aider les enseignants du préscolaire à comprendre le contexte culturel dans lequel s’opère le développement précoce du langage et de la faculté à lire et à écrire. Elle examine le rôle que les mères de familles chinoises et indiennes d’Amérique jouent dans l’émergence de l’apprentissage du lire et de l’écrire de leurs jeunes enfants au cours de leurs interactions quotidiennes. Vingt paires mère-enfant de chaque communauté ont participé à l’étude. Les résultats obtenus indiquent que les mères chinoises et indiennes d’Amérique diffèrent grandement dans l’aide qu’elles apportent à leurs enfants au cours du développement de l’apprentissage à lire et à écrire. les mères chinoises ont plus tendance à privilégier les interactions basées sur la chose imprimée que les mères indiennes d’Amérique. A l’inverse, ces dernières préferent baser leurs interactions sur des narrations orales portant sur la vie en général ainsi que sur leurs expériences personnelles. De plus, les mères des deux communautés privilégient différents aspects du développement précoce de l’écriture et de la lecture de leurs enfants. L’aide que les mères chinoises apportent à leurs enfants est plutôt explicite, élaborant et se concentrant sur des événements spécifiques, alors que les mères indiennes ont tendance à aider leurs enfants de façon implicite et en contexte. Il ressort de cette étude que les enseignants du préscolaire doivent impérativement comprendre le fonctionnement exact des mécanismes d’apprentissage du lire et de l’écrire dans des contextes différents, et ce afin d’optimiser le potentiel d’apprentissage de chaque enfant dans un environment éducatif préscolaire.

Optical properties of polycrystalline YBa2Cu3O7−−δ

Reflectivity of polycrystalline YBa2Cu3O7-δ has been measured in the energy ranges from 2.5 to 0.05 eV and from 27 to 3.7 meV at room temperature. A Drude edge due to the free electron has been observed at 1.4 eV and the carrier concentration is estimated as 3.2×1021 cm-3. The observed low reflectivity suggests the two dimensional character of the free electron. Below Tc a structure has been observed around 17.7 meV (143 cm-1), from which the energy gap 2Δ is tentatively estimated as 15.5 meV (125 cm-1) at 15 K. Alternatively, the structure may be due to a transverse collective excitation.

Responding to Children's Everyday Transgressions in Chinese Working-Class Families.

This study examines how working‐class mothers in the Peoples Republic of China respond to their young childrens transgressions in everyday contexts. Twenty 4‐year‐old children and their mothers in a working‐class neighbourhood were observed in their daily routines at home. When addressing childrens transgressions and socialising desirable behaviour, mothers frequently made references to other children, childrens media characters, past transgressions, authority figures and quotes from the classics. Moreover, the study indicates that mothers responded differently to some of the transgressions committed by boys as opposed to girls. This study also demonstrates that children understood social and moral rules by spontaneously elaborating on and appropriating the socialisation strategies used by their mothers.

Insights into the effect of thermocapillary migration of droplet on lubrication

Thermocapillary migration, as a liquid lubricant loss mechanism, will lead to the failures of moving mechanical assemblies due to lack of lubricant. The purpose of this study was to determine the influence of thermocapillary migration of droplet on surface lubrication properties. An experimental set-up was designed to investigate the migration behavior of paraffin oil driven by temperature gradient. Friction tests were carried out to evaluate the influences of lubricant migration on tribological performance. Aspects of the temperature gradient, oil volume and initial migrating time were taken into account. The experimental results showed that the increment of temperature gradient and oil drop volume can both enhance the average velocity of drop migration, while the average velocity decreases over time. Temperature gradient exhibits the dominated effect on surface lubrication properties and starvation first takes place at the highest temperature gradient. In addition, a transition of wear mechanism from an abrasive to adhesion wear is observed in particular situations.

Optical absorption of YBa2Cu3O7−δ and ErBa2Cu3O7−δ crystals due to interband transition

Reflectivity in the a-b plane of single crystals of orthorhombic YBa2Cu3O7-δ and ErBa2Cu3O7-δ has been measured at room temperature in the photon energy region from 0.05 to 30 eV and the spectra of absorption and energy loss function have been obtained by the Kramers-Kronig analysis. General features of the structure in the spectra of the Y-compound in the interband transition region from 1 to 8 eV are consistent with those calculated by Zhao et al. based on the energy band theory, but peaks in the observed absorption spectrum are shifted by 1 to 2 eV to the high energy side compared with the calculation.

Anisotropic Drude Reflectivity of Ag2F Crystal

Large single crystals of Ag 2 F have been grown and anisotropic electrical conductivity and optical reflectivity have been measured. The dc conductivity along the c -axis is about one tenth of that in the c -plane and its temperature dependence is metallic. Reflectivity spectra have been observed from 0.05 to 30 eV with linearly polarized light whose electric vectors are perpendicular and parallel to the c -axis. Clear anisotropic reflectivity due to the conduction electrons has been found with the sharp Drude edges at 2.9 and 0.9 eV in the perpendicular and parallel directions, respectively. The analysis of the results does not give a quantitative support to the two Fermi surface model proposed by Hamada et al . Absorption spectra in the interband transition region above the Drude edges also show anisotropy.