结合限制密集轨迹与时空共生特征的行为识别

针对传统密集轨迹方法应用到真实场景后过多无效轨迹耗费存储与计算资源且严重影响有效特征提取的不足,提出一种新的人体行为识别算法。首先,检测视频帧中存在的人体目标并对获得的包含人体的矩形框进行扩展,利用扩展后的矩形框对传统密集采样特征点的范围进行筛选限制;然后,对筛选限制后的特征点在光流场中跟踪一定帧数获取限制密集轨迹,并在以限制密集轨迹为中心的时空体内构建一组包含轨迹的空间位置、时空上下文信息的特征描述子;最后在视觉词袋模型框架下,采用SVM对特征向量进行编码分类。结果显示:在KTH、YouTube和HMDB51 3个行为数据库上的识别准确率分别达到98.1%、89.7%和66.9%。证明本算法对复杂真实场景中的人体行为具有较高的识别能力。     

Towards the ‘ubiquitous eco-city’: An analysis of the internationalisation of eco-city policy and practice

European governments are tending to perceive cities as sites of renewed economic dynamism and physical renaissance, and as places that can help to resolve social and environmental challenges. The paper presents three propositions for why the fortunes of cities in advanced economies may have improved. It then offers evidence from across Western Europe to assess whether they have done so, both in comparison with their past trajectories and in relation to smaller urban and rural areas. One finding is that cities in aggregate have experienced continued prosperity rather than decline and revival or accelerated growth. Another is that their overall position relative to smaller settlements does not seem to have changed greatly. Looking in more detail, however, there is more evidence of resurgence, as well as the opposite. National variations seem important and cities in Finland, Sweden, Ireland, Britain and Spain show signs of substantial economic improvement over the last decade. In contrast, cities in Germany have experienced a marked slowdown, albeit from a position of comparative prosperity at the outset.     

Flexibility of bacterial flagella in external shear results in complex swimming trajectories

Many bacteria use rotating helical flagella in swimming motility. In the search for food or migration towards a new habitat, bacteria occasionally unbundle their flagellar filaments and tumble, leading to an abrupt change in direction. Flexible flagella can also be easily deformed by external shear flow, leading to complex bacterial trajectories. Here, we examine the effects of flagella flexibility on the navigation of bacteria in two fundamental shear flows: planar shear and Poiseuille flow realized in long channels. On the basis of slender body elastodynamics and numerical analysis, we discovered a variety of non-trivial effects stemming from the interplay of self-propulsion, elasticity and shear-induced flagellar bending. We show that in planar shear flow the bacteria execute periodic motion, whereas in Poiseuille flow, they migrate towards the centre of the channel or converge towards a limit cycle. We also find that even a small amount of random reorientation can induce a strong response of bacteria, leading to overall non-periodic trajectories. Our findings exemplify the sensitive role of flagellar flexibility and shed new light on the navigation of bacteria in complex shear flows.     

How trajectories of reasons for alcohol use relate to trajectories of binge drinking: National panel data spanning late adolescence to early adulthood.

Developmental changes in both alcohol use behaviors and self-reported reasons for alcohol use were investigated. Participants were surveyed every 2 years from ages 18 to 30 as part of the Monitoring the Future national study (analytic weighted sample size N = 9,308; 53% women, 40% college attenders). Latent growth models were used to examine correlations between trajectories of binge drinking and trajectories of self-reported reasons for alcohol use across young adulthood. Results revealed developmental changes in reasons for use and correlations between the patterns of within-person change in frequency of binge drinking and within-person change in reasons for use. In particular, an increase in binge drinking between ages 18 and 22 was most positively correlated with slopes of using alcohol to get high and because of boredom. Continued binge drinking between ages 22 and 30 was most strongly correlated with using alcohol to get away from problems. Almost no moderation by gender, race, college attendance, employment, or marital status was found. Binge drinking and reasons for alcohol use traveled together, illustrating the ongoing and dynamic connections between changes in binge drinking and changes in reasons for use across late adolescence and early adulthood. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Gender differences in the development and adult outcome of co-occurring depression and delinquency in adolescence.

Using a dual trajectory modeling approach, we examined co-occurring trajectories of depression and delinquency from age 11 to age 18 and their relation to adult outcome six years later in a community sample of 1423 (674 boys) adolescents. We also examined the effects of childhood externalizing, internalizing, and social problems on trajectory membership for depression and delinquency. The results showed that although more girls than boys were likely to follow high-level, co-occurring trajectories on depression and delinquency, the adult outcome of adolescents following high-level trajectories on both domains was poorer for boys than for girls. However, the combination of decreasing depression symptoms and increasing delinquency symptoms across adolescence was related with poorer adult outcomes for girls compared to boys. Finally, whereas boys' high-level co-occurring trajectory of depression and delinquency was predicted by childhood aggression, girls' equivalent trajectory was predicted by childhood depression and delinquency. The findings support the “gender paradox” effect (Loeber & Keenan, 1994) stating that in disorders with an unequal gender ratio, members of the gender with the lower prevalence rate tend to be more seriously affected in terms of comorbidity and poor outcome. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Alcohol use trajectories and the ubiquitous cat's cradle: Cause for concern?

[Correction Notice: An erratum for this article was reported in Vol 120(2) of Journal of Abnormal Psychology (see record 2011-05801-001). Due to formatting problems, some of the data and graphic information in the original Figure 7 are not correctly displayed. Although not all data in the original Figure 7 are visible, nothing displayed in that figure was in error.] In recent years, trajectory approaches to characterizing individual differences in the onset and course of substance involvement have gained popularity. Previous studies have sometimes reported 4 prototypic courses: (a) a consistently “low” group, (b) an “increase” group, (c) a “decrease” group, and (d) a consistently “high” group. Although not always recovered, these trajectories are often found, despite these studies varying in the ages of the samples studied and the duration of the observation periods employed. Here, the authors examined the consistency with which these longitudinal patterns of heavy drinking were recovered in a series of latent class growth analyses that systematically varied the age of the sample at baseline, the duration of observation, and the number and frequency of measurement occasions. Data were drawn from a 4-year, 8-wave panel study of college student drinking (N = 3,720). Despite some variability across analyses, there was a strong tendency for these prototypes to emerge regardless of the participants' age at baseline and the duration of observation. These findings highlight potential problems with commonly employed trajectory-based approaches and the need to not over-reify these constructs. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

瞬变载荷作用下滑动轴承轴心轨迹计算仿真

为了研究动压滑动轴承在瞬变载荷作用下的润滑状况,在考虑轴颈惯性力和非线性油膜力的基础上,建立了滑动轴承轴心轨迹的运动方程,提出了采用欧拉法求解有限长滑动轴承瞬时轴心轨迹的数值方法。分别计算了在阶跃、矩形脉冲和正弦脉冲瞬变载荷作用下轴心轨迹、最大油膜压力及最小油膜厚度的变化规律。分析结果表明,在瞬变载荷作用时,轴心轨迹、最大油膜压力及最小油膜厚度都有较大的变化并呈现出一定的振荡过程。由于脉冲载荷的作用时间有限,随着其消失,轴心乃收敛于原平衡位置,而阶跃载荷则使轴心收敛于新的平衡位置。     

évolution du trouble d’opposition et du trouble des conduites au cours de l’enfance.

This study aimed at describing the evolution of the symptoms of the oppositional disorder and conducts disorder on a 4-year period (3 times of measurement), depending on whether both disorders appear simultaneously or separately. The sample was composed of 336 children (6–13 years-old), separated in three groups according to the nature of the disorder they presented at the beginning of the study: oppositional disorder only, conducts disorder only, both oppositional and conducts disorders. Structured diagnostic interviews based on the diagnostic criterions of the Diagnostic and Statistical Manual of Mental Disorders (4 éd., texte rév.; American Psychiatric Association, 2000) were used in order to evaluate the average number of symptoms associated to each disorder at each time of measurement. Multilevel regression analysis suggest that the initial co-occurrence of the disorders is neither associated to the evolution of the symptoms of the conducts disorder nor to those of the oppositional disorder. However, this co-occurrence, that can also include the attention-deficit/hyperactivity disorder, can increase the number of symptoms in children, which likely contributes to maintain the diagnostics in some cases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Links between friendship relations and early adolescents’ trajectories of depressed mood.

The present study examined to what extent different types of friendship experiences (i.e., friendlessness, having depressed friends, and having nondepressed friends) are associated with early adolescents’ longitudinal trajectories of depressed mood. On the basis of a sample of 201 youths (108 girls, 93 boys), we identified 3 distinct longitudinal profiles of depressed mood from Grade 5 (age 11) through Grade 7 (age 13): one group with consistently low levels of depressed mood, another group showing a sharp increase in depressed mood from late childhood through early adolescence, and a 3rd group with consistently high levels of depressed mood from late childhood through early adolescence. Subsequent analyses revealed that, compared to friendless youths, youths with nondepressed friends showed less elevated trajectories of depressed mood, whereas youths with depressed friends showed more elevated trajectories. The theoretical and practical implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Longitudinal predictors of reading and math trajectories through middle school for African American versus Caucasian students across two samples.

This study's primary purpose was to examine the relative contribution of social-behavioral predictors to reading and math skills. The study expands on Duncan et al.'s (2007) work by using longitudinal methodology from the National Institute of Child Health and Human Development's Study of Child Care and Youth Development (SECCYD) and the Early Childhood Longitudinal Study, Kindergarten Class of 1998–1999 (ECLS-K) databases, and by focusing on potential differences in patterns of early predictors of later reading and math trajectories for African American versus Caucasian students. Predictor measures were selected at kindergarten, and the outcomes included standardized reading and math scores obtained from Grades 1, 3, 5, and 9 for the SECCYD sample, and Grades 3, 5, and 8 for the ECLS-K sample. Consistent with Duncan et al.'s findings, results reflect the relative contributions of early reading and math skills to later functioning in these respective academic domains for both samples, and there are indications for the importance of early expressive language skills to both reading and math in the SECCYD sample. Findings related to the power of social-behavioral predictors, however, are not consistent across samples. Although the SECCYD sample evidenced no such predictors, several interactions in the ECLS-K sample suggested the moderating effects of early ratings of aggressive behaviors and internalizing behaviors on later reading and math for African American students. The moderating effects of early teacher ratings of attention and internalizing behaviors for African American students as compared with Caucasian students in later math growth also were noted. The importance of early social-behavioral functions as related to later academic skills remains an important area of inquiry. (PsycINFO Database Record (c) 2010 APA, all rights reserved)