Search

The combined use of high resolution X-ray computed tomography with digital image correlation allows quantitative observations of the three-dimensional deformations that occur within a material when it is strained. In suitable microstructures, the displacement resolution is sub-voxel (a voxel is the three-dimensional equivalent of a pixel), and both elastic and plastic deformations can be studied. This paper reviews recent work in which three-dimensional in situ observations of deformation have provided unique insights that support both continuum and heterogeneous microstructure-dependent models of damage development in a range of materials. The examples presented include; crack propagation in a quasi-brittle porous material (polygranular graphite), sub-indentation radial and lateral cracking in a brittle polycrystalline ceramic (alumina); plastic deformation and damage development underneath indentations in a ductile metal (Al-SiC composite) and a ceramic matrix composite (SiC-SiCfibre). These examples show how material properties can be obtained by analysis of the displacement fields, how such measurements can be used to better define the applied loading on small test specimens and how crack opening magnitude and mode may be extracted also. Some new directions for research are outlined, including the combined use of diffraction and imaging techniques on synchrotron X-ray facilities to map both elastic and inelastic strains.

The authors of this study tested a selection-influence-de-selection model of depression. This model explains friendship influence processes (i.e., friends' depressive symptoms increase adolescents' depressive symptoms) while controlling for two processes: friendship selection (i.e., selection of friends with similar levels of depressive symptoms) and friendship de-selection (i.e., de-selection of friends with dissimilar levels of depressive symptoms). Further, this study is unique in that these processes were studied both inside and outside the school context. The authors used a social network approach to examine 5 annual measurements of data in a large (N =847) community-based network of adolescents and their friends (M = 14.3 years old at first measurement). Results supported the proposed model: adolescents tend to select friends with similar levels of depression, and friends may increase each other's depressive symptoms as relationships endure. These two processes were most salient outside the school context. At the same time, friendships seemed to be ended more frequently if adolescents' level of depressive symptoms was dissimilar to that of their friends.

When analyzing repeated measurements data, researchers often have expectations about the relations between the measurement means. The expectations can often be formalized using equality and inequality constraints between (i) the measurement means over time, (ii) the measurement means between groups, (iii) the means adjusted for time-invariant covariates, and (iv) the means adjusted for time-varying covariates. The result is a set of informative hypotheses. In this paper, the Bayes factor is used to determine which hypothesis receives most support from the data. A pivotal element in the Bayesian framework is the specification of the prior. To avoid subjective prior specification, training data in combination with restrictions on the measurement means are used to obtain so-called constrained posterior priors. A simulation study and an empirical example from developmental psychology show that this prior results in Bayes factors with desirable properties.

The current study examined the longitudinal associations of time spent on Internet activities for communication purposes (i.e., IM-ing) versus time spent on Internet activities for non-communication purposes (i.e., surfing) with depression and social anxiety, as well as the moderating role of perceived friendship quality in these associations. Questionnaire data were gathered from 307 Dutch middle adolescents (average age 15 years) on two waves with a one-year interval. For adolescents who perceive low friendship quality, Internet use for communication purposes predicted less depression, whereas Internet use for non-communication purposes predicted more depression and more social anxiety. These results support social compensation effects of IM-ing on depression and poor-get-poorer effects of surfing on depression and social anxiety, respectively.

In dit onderzoek zijn bij 307 adolescenten (gemiddelde leeftijd 15 jaar) de longitudinale effecten van internetgebruik op internaliserend probleemgedrag onderzocht. Daarbij is onderscheid gemaakt tussen internetgebruik gericht op communicatie (‘chatten’) en internetgebruik niet gericht op communicatie (‘surfen’). Tevens is de modererende rol van de kwaliteit van de beste vriendschap in de effecten van internetgebruik op probleemgedrag onderzocht. De resultaten geven aan dat voor adolescenten met een lage kwaliteit van vriendschap langer chatten minder internaliserende problemen voorspelt, terwijl in die groep langer surfen juist meer internaliserende problemen voorspelt. De resultaten leveren ondersteuning voor de associatie tussen eerder internetgebruik en latere toenemende of afnemende internaliserende problemen, maar kunnen niet automatisch geïnterpreteerd worden in termen van causale verbanden tussen internetgebruik en latere internaliserende problemen.

The current study aimed to provide more insight into the role of online chatting in young adults’ emotional adjustment. A model was tested that takes into account (a) extraversion of individuals who communicate online, (b) the kind of peers these individuals communicate with online (i.e., online-exclusive peers vs. friends), and (c) the extent to which effects of online chatting on emotional adjustment are mediated by individuals’ ability to provide support to others. Young adults (age M = 18.9) filled out questionnaires about themselves and their fellow students at three measurements with a 4-month interval. Results showed that only for less extraverted individuals, chatting with peers found exclusively online directly predicted higher self-esteem and indirectly predicted less depressive symptoms through increases in supportiveness. Thus, results supported a model of social compensation where effects of online chatting with online-exclusive peers improved young adults’ emotional adjustment.

The current study aimed to provide more insight into the role of online chatting in young adults’ emotional adjustment. A model was tested that takes into account (a) extraversion of individuals who communicate online, (b) the kind of peers these individuals communicate with online (i.e., online-exclusive peers vs. friends), and (c) the extent to which effects of online chatting on emotional adjustment are mediated by individuals’ ability to provide support to others. Young adults (age M = 18.9) filled out questionnaires about themselves and their fellow students at three measurements with a 4-month interval. Results showed that only for less extraverted individuals, chatting with peers found exclusively online directly predicted higher self-esteem and indirectly predicted less depressive symptoms through increases in supportiveness. Thus, results supported a model of social compensation where effects of online chatting with online-exclusive peers improved young adults’ emotional adjustment.

The current study investigated the mechanisms underlying peer contagion of depressive symptoms in adolescence. Five annual measurements of data were gathered from a large (N = 842) community-based network of adolescents (M = 14.3 years at first measurement). Results showed that, after controlling for selection and deselection of friends on the basis of depressive symptoms, peers' depressive symptoms predicted increases in adolescents' depressive symptoms over time. Failure anticipation mediated effects of peers' depressive symptoms on adolescents' depressive symptoms, particularly for girls. Thus, results suggest that peers' depressive symptoms place adolescents at risk of developing depressive symptoms through increasing in failure anticipation.

The current dissertation focused on processes of friendship formation and friendship socialization in adolescence. The role of individual characteristics in friendship formation were examined at the a) individual level (individuals’ perceptions and traits), b) dyadic level (similarity between two persons in traits and preferences), and c) group level (peers’ perceptions of traits). For friendship socialization, we examined the relative importance of friends’ behaviors and perceptions of friendships in the behavioral and emotional development of adolescents. Data were used from two longitudinal projects, CONAMORE and My First Year. In CONAMORE, questionnaires were filled out both at school and at home. Data were used up to five annual measurements, spanning from early to late adolescence. From this project, several subsamples of adolescents and their friends were used. Questionnaires concerned friendship nominations, personality traits, media use, problem behaviors, and perceptions of friendship quality. In the My First Year project, 205 just-acquainted University freshmen filled out online questionnaires in five monthly measurements. In this project, friendship intensity, Big Five personality traits, and communication were examined using a longitudinal round-robin design. Findings regarding friendship formation indicate that individual characteristics have unique functions in friendship formation. On the individual level, Extraversion and Agreeableness predicted selecting others more and being selected by others more, respectively. Moreover, whereas adolescents’ perceptions of similarity in overall personality traits predicted more friendship intensity, actual similarity in these traits did not. Friendship intensity, in turn, predicted perceptions of more similarity in overall personality traits. On the dyadic level, adolescents tended to form friendships with others who were similar in specific personality traits Extraversion, Agreeableness, and Openness. Further, similarity in specific and overall music preferences predicted friendship formation. On the group level, peers’ perceptions of similarity between just-acquainted late adolescents predicted the frequency they communicated. This, in turn, predicted friendship intensity over time. Support was found for salient functions of friends’ behaviors and perceptions of friendship in the development of individual characteristics. Whereas friends’ delinquent behaviors predicted increases in boys’ delinquent behaviors from early to middle adolescence, perceptions of closeness in friendships did not. For girls, however, perceptions of higher closeness and higher individuality were associated with lower levels of depression from early to late adolescence. Only for adolescents who perceive low closeness in friendships, non-communication based Internet use predicted more depression and social anxiety over time. For adolescents who perceive medium to high closeness, Internet use did not predict depression and social anxiety. In sum, perceptions of friendship quality and friends’ behaviors both seem to have unique functions in behavioral problems for boys and emotional problems for both boys and girls, respectively. Thus, both adolescents themselves and others seem to have an important role in adolescents’ friendships and adolescents’ development. Adolescents’ own individual traits and preferences tend to partially determine their friendship choices. Moreover, adolescents’ perceptions of others’ personality may be more consequential for their friendship choices than how others’ personality actually is. Nevertheless, peers’ perceptions and friends’ behaviors may additionally influence adolescents’ friendship selection and behavioral and emotional development.

The current study examined the longitudinal associations of time spent on Internet activities for communication purposes (i.e., IM-ing) versus time spent on Internet activities for non-communication purposes (i.e., surfing) with depression and social anxiety, as well as the moderating role of perceived friendship quality in these associations. Questionnaire data were gathered from 307 Dutch middle adolescents (average age 15 years) on two waves with a one-year interval. For adolescents who perceive low friendship quality, Internet use for communication purposes predicted less depression, whereas Internet use for non-communication purposes predicted more depression and more social anxiety. These results support social compensation effects of IM-ing on depression and poor-get-poorer effects of surfing on depression and social anxiety, respectively.

The present study examines the role of similarity in music preferences in the formation and discontinuation of friendships over a 1-year period. Questionnaire data were gathered from 283 Dutch same-sex mutual best friends (mean age=12.97) in two waves with a 1-year interval. Results show consistent evidence for high similarity in specific music dimensions among friends at both waves. Moderate similarity was found in the overall patterning of preferences for music genres at both waves, even after controlling for similarity in social background. Specific music similarity in more non-mainstream music dimensions and overall music similarity at Wave 1 were related to selecting a new friend at Wave 2. However, similarity in music preferences was not related to the discontinuation of an existing friendship at Wave 2. Thus, results suggest that similarity in music preferences is related to friendship formation, and not to friendship discontinuation.

This study examined friendship types in developmental trajectories of perceived closeness and balanced relatedness. In addition, differences between friendship types in the development of constructive problem solving and depression were examined. Questionnaire data of five annual waves were used from two adolescent cohorts (cohort 1: M = 12.41 years; cohort 2: M = 16.37 years). Growth Mixture Modeling revealed two developmental trajectories in cognitive representations of perceived friendship intimacy: interdependent and disengaged friendships. Adolescents in interdependent friendships were characterized by high perceived closeness and balanced relatedness across adolescence. Furthermore, adolescents in disengaged friendships had lower levels of and smaller increases in constructive problem solving. Girls in disengaged friendships showed smaller increases in balanced relatedness and higher levels of depression than boys in disengaged friendships and adolescents in interdependent friendships.

The present study examines the role of similarity in music preferences in the formation and discontinuation of friendships over a 1-year period. Questionnaire data were gathered from 283 Dutch same-sex mutual best friends (mean age=12.97) in two waves with a 1-year interval. Results show consistent evidence for high similarity in specific music dimensions among friends at both waves. Moderate similarity was found in the overall patterning of preferences for music genres at both waves, even after controlling for similarity in social background. Specific music similarity in more non-mainstream music dimensions and overall music similarity at Wave 1 were related to selecting a new friend at Wave 2. However, similarity in music preferences was not related to the discontinuation of an existing friendship at Wave 2. Thus, results suggest that similarity in music preferences is related to friendship formation, and not to friendship discontinuation.

The authors examined associations of perceived similarity, actual similarity, and peer-rated similarity in personality with friendship intensity during the acquaintanceship process in a naturalistic setting. Self- and peer-rated personality data were gathered from undergraduates (mean age = 18.9) at 5 time points during the first year of university using a round-robin design. Whereas perceived similarity and peer-rated similarity in personality were concurrently associated with more friendship intensity for just-acquainted individuals, actual similarity in personality was not. Further, bidirectional cross-lagged associations between perceived similarity and friendship intensity were found. Peer-rated similarity was also associated with increases in friendship intensity, and this association was mediated by communication frequency. These results indicate that specific types of similarity in personality are differentially associated with friendship intensity during early phases of acquaintanceship in a real-life setting. Further, insight was provided in the direction of causality between similarity and attraction: Perceived and peer-rated similarity seem to breed friendship intensity, whereas friendship intensity seems to breed perceived similarity only. Finally, peers' expectations seem to affect individuals' communicative behaviors, which in turn affect friendship formation.

The present study examines both the unique and the combined role of best friends’ delinquency and perceived friendship quality in the development of adolescent delinquency. Questionnaire data were gathered from 435 Dutch adolescent best friends (mean age at first wave = 12.97) over a period of 5 years with annual assessments. Results showed that mean levels of delinquency and perceived friendship quality increased over time. Adolescent best friends were highly similar in both mean levels and changes in delinquency over time. For boys, similarity in mean level delinquency between best friends was higher than for girls. In addition, only for boys, friends’ delinquency is associated with increases in adolescent delinquency over time, and adolescents’ delinquency is associated with increases in friends’ delinquency over time. No bidirectional longitudinal associations were found between perceived friendship quality and adolescent delinquency. No interaction effects between friendship quality and friends’ delinquency on adolescent delinquency were found. Thus, findings were more in support of the differential association theory than of the social control theory.

The present study examines the role of similarity in music preferences in the formation and discontinuation of friendships over a one-year period. Questionnaire data were gathered from 283 Dutch same-sex mutual best friends (Mean age = 12.97) in two waves with a one-year interval. Results show consistent evidence for high similarity in specific music dimensions among friends at both waves. Moderate similarity was found in the overall patterning of preferences for music genres at both waves, even after controlling for similarity in social background. Girls were found to be more similar in their preference for Rock than boys. Specific music similarity in more non-mainstream music dimensions and overall music similarity at Wave 1 were related to selecting a new friend at Wave 2. However, similarity in music preferences was not related to the discontinuation of an existing friendship at Wave 2. Thus, results suggest that similarity in music preferences is related to friendship formation, and not to friendship discontinuation.

In dit onderzoek zijn bij 307 adolescenten (gemiddelde leeftijd 15 jaar) de longitudinale effecten van internetgebruik op internaliserend probleemgedrag onderzocht. Daarbij is onderscheid gemaakt tussen internetgebruik gericht op communicatie (‘chatten’) en internetgebruik niet gericht op communicatie (‘surfen’). Tevens is de modererende rol van de kwaliteit van de beste vriendschap in de effecten van internetgebruik op probleemgedrag onderzocht. De resultaten geven aan dat voor adolescenten met een lage kwaliteit van vriendschap langer chatten minder internaliserende problemen voorspelt, terwijl in die groep langer surfen juist meer internaliserende problemen voorspelt. De resultaten leveren ondersteuning voor de associatie tussen eerder internetgebruik en latere toenemende of afnemende internaliserende problemen, maar kunnen niet automatisch geïnterpreteerd worden in termen van causale verbanden tussen internetgebruik en latere internaliserende problemen.

The purpose of this study was to examine dyadic similarity among mutual adolescent best friends and the moderating role of gender in this similarity. Questionnaire data were gathered from 267 Dutch adolescent same-sex best friends (mean age = 14.58). Results showed that both boys and girls were found to be more similar to their mutual best friend in the Big Five personality traits extraversion and agreeableness. Furthermore, only girls were more similar to their mutual best friend than randomised pairs in problem behaviour and perceived relationship characteristics. In general, similarity seems to play a larger role in mutual best friendships between girls than between boys.

The present study examines both the unique and the combined role of best friends’ delinquency and perceived friendship quality in the development of adolescent delinquency. Questionnaire data were gathered from 435 Dutch adolescent best friends (mean age at first wave = 12.97) over a period of 5 years with annual assessments. Results showed that mean levels of delinquency and perceived friendship quality increased over time. Adolescent best friends were highly similar in both mean levels and changes in delinquency over time. For boys, similarity in mean level delinquency between best friends was higher than for girls. In addition, only for boys, friends’ delinquency is associated with increases in adolescent delinquency over time, and adolescents’ delinquency is associated with increases in friends’ delinquency over time. No bidirectional longitudinal associations were found between perceived friendship quality and adolescent delinquency. No interaction effects between friendship quality and friends’ delinquency on adolescent delinquency were found. Thus, findings were more in support of the differential association theory than of the social control theory.