Compressive Strength of Hydrostatic-Stress-Sensitive Materials at High Strain-Rates

Many engineering materials demonstrate dynamic enhancement of their compressive strength with the increase of strain-rate, which have been included in material models to improve the reliability of numerical simulations of the material and structural responses under impact and blast loads. The strain-rate effects on the dynamic compressive strength of a range of engineering materials which behave in hydrostatic-stress-sensitive manner were investigated. It is concluded that the dynamic enhancement of the compressive strength of a hydrostatic-stress-sensitive material may include inertia-induced lateral confinement effects, which, as a non-strain-rate factor, may greatly enhance the compressive strength of these materials. Some empirical formulae based on the dynamic stress-strain measurements over-predict the strain-rate effects on the compressive strength of these hydrostatic-stress-sensitive materials, and thus may over-estimate the structural resistance to impact and blast loads, leading to non-conservative design of protective structures.     

“我不能”的葬礼

常言道:失败乃成功之母。这也是我们在失败时经常用来鼓励自己继续前行的话。如果说这句话略带点阿Q,是精神胜利法的话,那么下面这则小故事则给人置之死地而后生的破釜沉舟的勇气和力量。细细品味吧!     

Inhibitory Control Across the Preschool Years: Developmental Changes and Associations with Parenting

The normative developmental course of inhibitory control between 2.5 and 6.5 years, and associations with maternal and paternal sensitivity and intrusiveness were tested. The sample consisted of 383 children (52.5% boys). During four annual waves, mothers and fathers reported on their children’s inhibitory control using the Children's Behavior Questionnaire. During the first wave, mothers’ and fathers’ sensitivity and intrusiveness were observed and coded with the Emotional Availability Scales. Inhibitory control exhibited partial scalar invariance over time, and increased in a decelerating rate. For both mothers and fathers, higher levels of sensitivity were associated with a higher initial level of children's inhibitory control, whereas higher levels of intrusiveness predicted a slower increase in children's inhibitory control.     

Prenatal Neighborhood Ethnocultural Context and the Mental Health of Mothers and Children in Low-Income Mexican American Families

Socioeconomically disadvantaged neighborhoods increase the risk for poor mental health among residents, yet protective factors may operate alongside risk. This study evaluated the influence of the prenatal neighborhood ethnocultural context on child behavior problems and maternal depressive symptoms. Prenatal maternal role expectations, prenatal culture-specific stress, and postpartum depression (PPD) symptoms were evaluated as mediators. Participants included 322 low-income, Mexican American mother-child dyads. Women (M_age = 27.8) reported on proposed mediators, maternal depressive symptoms, and child behavior problems at 4.5 years. Neighborhood Latinx concentration was obtained from census data. Higher Latinx concentration predicted fewer maternal depressive symptoms and child behavior problems, mediated through role expectations and PPD symptoms. Results suggest prenatal neighborhood context to impact later maternal and child mental health.     

Incorporating Uncertainty Into Parallel Analysis for Choosing the Number of Factors via Bayesian Methods

A number of psychometricians have suggested that parallel analysis (PA) tends to yield more accurate results in determining the number of factors in comparison with other statistical methods. Nevertheless, all too often PA can suggest an incorrect number of factors, particularly in statistically unfavorable conditions (e.g., small sample sizes and low factor loadings). Because of this, researchers have recommended using multiple methods to make judgments about the number of factors to extract. Implicit in this recommendation is that, when the number of factors is chosen based on PA, uncertainty nevertheless exists. We propose a Bayesian parallel analysis (B-PA) method to incorporate the uncertainty with decisions about the number of factors. B-PA yields a probability distribution for the various possible numbers of factors. We implement and compare B-PA with a frequentist approach, revised parallel analysis (R-PA), in the contexts of real and simulated data. Results show that B-PA provides relevant information regarding the uncertainty in determining the number of factors, particularly under conditions with small sample sizes, low factor loadings, and less distinguishable factors. Even if the indicated number of factors with the highest probability is incorrect, B-PA can show a sizable probability of retaining the correct number of factors. Interestingly, when the mode of the distribution of the probabilities associated with different numbers of factors was treated as the number of factors to retain, B-PA was somewhat more accurate than R-PA in a majority of the conditions.     

Teacher Depressive Symptoms and Child Math Achievement in Head Start: The Roles of Family–Teacher Relationships and Approaches to Learning

This study examined the direct and indirect associations of teachers’ depressive symptoms with children’s math achievement through teachers’ reports of family–teacher relationships and children’s approaches to learning (ATL) in Head Start. This study included 3- and 4-year-old 1,547 children (49% female; 27% White, 24% Black, 41% Hispanic/Latino, and 8% others) who attended Head Start from fall 2014 through spring 2015. Results indicated that teachers’ depressive symptoms were directly associated with lower gains in children’s math skills over a year. In addition, teachers who reported higher depressive symptoms were less likely to report positive family–teacher relationships. This, in turn, resulted in lower gains in children’s ATL and was associated with lower achievement in math skills (r² = .69).     

The relationship between child behaviour problems at school entrance and teenage vocabulary acquisition: A comparison of two generations of British children born 30 years apart

Behaviour problems in early childhood have a lasting impact on cognitive development and education attainment in later adolescence and into adulthood. Here we address the relationship conduct and hyperactivity problems at school entrance, and vocabulary acquisition in adolescence. We compare performance in identical assessments across two generations of British children born 30 years apart in 1970 (n = 15,676) and 2000/2 (n = 16,628) and find that both conduct and hyperactivity problems have a negative association with later vocabulary in both generations. We take advantage of rich longitudinal birth cohort data and establish that these relationships hold once family socioeconomic status and a child’s personal characteristics and earlier vocabulary acquisition are taken into account. We also find that teenagers today achieved substantively lower scores in the vocabulary assessment compared to their counterparts born 30 years earlier, and that this holds across all categories within each of the family and individual characteristics considered in this article. As vocabulary and language skills are key prerequisites for wider learning, we discuss implications the findings have for education policies.     

On the dynamic stability of an axially oscillating beam

Dynamic problems of axially moving materials as exemplified by strings in textile industry and band saws, belts and chains in mechanical machinery have recently received some attention (1–15). In the present study, the parametric resonance of an axially accelerated beam is investigated. The beam which has encastré ends is subjected to a periodic root force as shown in Fig. 1. The object of the investigation is to identify regions of instability of this system for various combinations of the excitation frequency and amplitude of the axial oscillations.