Origin of giant enhancement of phase contrast in electron holography of modulation-doped n-type GaN.

The electron optical phase contrast probed by electron holography at n-n+ GaN doping steps is found to exhibit a giant enhancement, in sharp contrast to the always smaller than expected phase contrast reported for p-n junctions. We unravel the physical origin of the giant enhancement by combining off-axis electron holography data with self-consistent electrostatic potential calculations. The predominant contribution to the phase contrast is shown to arise from the doping dependent screening length of the surface Fermi-level pinning, which is induced by FIB-implanted carbon point defects below the outer amorphous shell. The contribution of the built-in potential is negligible for modulation doping and only relevant for large built-in potentials at e.g. p-n junctions. This work provides a quantitative approach to so-called dead layers at TEM lamellas.

Cooperative Conformational Transitions Underpin the Activation Heat Capacity in the Temperature Dependence of Enzyme Catalysis.

Many enzymes display non-Arrhenius behavior with curved Arrhenius plots in the absence of denaturation. There has been significant debate about the origin of this behavior and recently the role of the activation heat capacity (ΔCP⧧) has been widely discussed. If enzyme-catalyzed reactions occur with appreciable negative values of ΔCP⧧ (arising from narrowing of the conformational space along the reaction coordinate), then curved Arrhenius plots are a consequence. To investigate these phenomena in detail, we have collected high precision temperature-rate data over a wide temperature interval for a model glycosidase enzyme MalL, and a series of mutants that change the temperature-dependence of the enzyme-catalyzed rate. We use these data to test a range of models including macromolecular rate theory (MMRT) and an equilibrium model. In addition, we have performed extensive molecular dynamics (MD) simulations to characterize the conformational landscape traversed by MalL in the enzyme-substrate complex and an enzyme-transition state complex. We have crystallized the enzyme in a transition state-like conformation in the absence of a ligand and determined an X-ray crystal structure at very high resolution (1.10 Å). We show (using simulation) that this enzyme-transition state conformation has a more restricted conformational landscape than the wildtype enzyme. We coin the term "transition state-like conformation (TLC)" to apply to this state of the enzyme. Together, these results imply a cooperative conformational transition between an enzyme-substrate conformation (ES) and a transition-state-like conformation (TLC) that precedes the chemical step. We present a two-state model as an extension of MMRT (MMRT-2S) that describes the data along with a convenient approximation with linear temperature dependence of the activation heat capacity (MMRT-1L) that can be used where fewer data points are available. Our model rationalizes disparate behavior seen for MalL and previous results for a thermophilic alcohol dehydrogenase and is consistent with a raft of data for other enzymes. Our model can be used to characterize the conformational changes required for enzyme catalysis and provides insights into the role of cooperative conformational changes in transition state stabilization that are accompanied by changes in heat capacity for the system along the reaction coordinate. TLCs are likely to be of wide importance in understanding the temperature dependence of enzyme activity and other aspects of enzyme catalysis.

Behavior of potentially toxic elements from stoker-boiler fly ash in Interior Alaska: paired batch leaching and solid-phase characterization.

Despite significant investigation of fly ash spills and mineralogical controls on the release of potentially toxic elements (PTEs) from fly ash, interactions with the surficial environment remain relatively poorly understood. We conducted 90-day batch leaching studies with paired analysis of supernatant and solid-phase mineralogy to assess the elemental release and transformation of fly ash upon reaction with aquatic media (18 MΩ cm-1 water and simulated rainwater). The fly ash in this study, collected from the University of Alaska Fairbanks stoker-boiler power plant, is high in unburned carbon (~20% LOI) and highly enriched in several PTEs relative to the upper continental crust. Supernatant concentrations of oxyanion-forming elements (e.g., As, Se, Mo, Sb) remained relatively low and constant, suggesting equilibrium with the solid phase, possibly ettringite [Ca6Al2(SO4)3(OH)12•26H2O], which is known to incorporate and sorb oxyanion-forming PTEs and was identified by X-ray diffraction. Synthetic precipitation leaching procedure (SPLP) results failed to capture important temporal trends. Lead and Ba supernatant concentrations consistently exceeded drinking water standards, as well as others upon exposure to simulated physiological solutions. Seven-day experiments with dissolved organic matter-isolate solutions indicated that for certain elements, liberation was influenced by carbon concentration and/or the identity of the isolate. Overall, this paired approach can serve as a model for future studies, bridging existing gaps between batch leaching and single-element mineralogical, sorption, or speciation studies.

Ultrafast-nonlinear ultraviolet pulse modulation in an AlInGaN polariton waveguide operating up to room temperature.

Ultrafast nonlinear photonics enables a host of applications in advanced on-chip spectroscopy and information processing. These rely on a strong intensity dependent (nonlinear) refractive index capable of modulating optical pulses on sub-picosecond timescales and on length scales suitable for integrated photonics. Currently there is no platform that can provide this for the UV spectral range where broadband spectra generated by nonlinear modulation can pave the way to new on-chip ultrafast (bio-) chemical spectroscopy devices. We demonstrate the giant nonlinearity of UV hybrid light-matter states (exciton-polaritons) up to room temperature in an AlInGaN waveguide. We experimentally measure ultrafast nonlinear spectral broadening of UV pulses in a compact 100 µm long device and deduce a nonlinearity 1000 times that in common UV nonlinear materials and comparable to non-UV polariton devices. Our demonstration promises to underpin a new generation of integrated UV nonlinear light sources for advanced spectroscopy and measurement.

State and Trait Mindfulness as Predictors of Skin Conductance Response to Stress.

Mindfulness is typically understood as non-judgmental, focused attention on the present moment, although it may be conceptualized as a state, a trait, and an outcome of intervention. There is a limited understanding of the physiological effects of state and trait mindfulness, and it has been a challenge to the research community to measure these effects. This study examined whether state and trait mindfulness are associated with reduced stress response activation in healthy young adults. Fifty-four undergraduate participants completed self-ratings of state and trait mindfulness, and continuous measures of psychophysiological reactivity (i.e., skin conductance response) before, during, and after an interview about a recurrent stressor. Results indicated that individuals with greater self-reported state mindfulness had lower sympathetic psychophysiological activation than those with lower state mindfulness. Moreover, those with greater self-reported state mindfulness experienced greater drops in psychophysiological activation following a stressful task. However, differences in psychophysiological activation were not evident when comparing those with higher and lower self-reported trait mindfulness. The findings suggest that state mindfulness, or "being in the moment", rather than trait mindfulness results in less engagement of metabolically costly psychophysiological activation in response to stress. Thus, intentional mindfulness during a stressful event may be important for decreasing sympathetic activation, resulting in lower bodily stress.

The Effectiveness of Mindfulness-Based Therapies for ADHD: A Meta-Analytic Review.

Objective: Mindfulness-based therapies (MBTs) have been shown to be efficacious in treating internally focused psychological disorders (e.g., depression); however, it is still unclear whether MBTs provide improved functioning and symptom relief for individuals with externalizing disorders, including ADHD. To clarify the literature on the effectiveness of MBTs in treating ADHD and to guide future research, an effect-size analysis was conducted. Method: A systematic review of studies published in PsycINFO, PubMed, and Google Scholar was completed from the earliest available date until December 2014. Results: A total of 10 studies were included in the analysis of inattention and the overall effect size was d = -.66. A total of nine studies were included in the analysis of hyperactivity/impulsivity and the overall effect was calculated at d = -.53. Conclusion: Results of this study highlight the possible benefits of MBTs in reducing symptoms of ADHD.

Using ecological momentary assessments to evaluate extant measures of mind wandering.

Mind wandering is a commonly experienced phenomenon. Although self-report measures are available to assess these attentional lapses, examination of their correspondence with the reported frequency of these episodes in daily life is warranted. Using ecological momentary assessments (EMAs), the present study aimed to validate 3 mind-wandering measures: the Mind-Wandering Questionnaire (MWQ) and the Mind Wandering-Spontaneous (MW-S) and Mind Wandering-Deliberate (MW-D) measures in university students (N = 100). Participants completed a series of questionnaires in an in-lab session. Using time-based EMA sampling, participants received 6 prompts via text message daily for 7 days. Each prompt asked students to report if their current thoughts were about something other than what they were doing using a scale ranging from completely on-task to completely on unrelated concerns. Self-report data collected via EMA indicated that reporting more mind-wandering episodes was associated with higher MWQ and MW-S scores but was not significantly correlated with the MW-D score. Results highlight the utility of EMA in validating measures designed to capture mind-wandering episodes. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Adolescent mental health and behavioural predictors of being NEET: a prospective study of young adults not in employment, education, or training.

BACKGROUND: Young adults who are not in employment, education, or training (NEET) are at risk of long-term economic disadvantage and social exclusion. Knowledge about risk factors for being NEET largely comes from cross-sectional studies of vulnerable individuals. Using data collected over a 10-year period, we examined adolescent predictors of being NEET in young adulthood. METHODS: We used data on 1938 participants from the Victorian Adolescent Health Cohort Study, a community-based longitudinal study of adolescents in Victoria, Australia. Associations between common mental disorders, disruptive behaviour, cannabis use and drinking behaviour in adolescence, and NEET status at two waves of follow-up in young adulthood (mean ages of 20.7 and 24.1 years) were investigated using logistic regression, with generalised estimating equations used to account for the repeated outcome measure. RESULTS: Overall, 8.5% of the participants were NEET at age 20.7 years and 8.2% at 24.1 years. After adjusting for potential confounders, we found evidence of increased risk of being NEET among frequent adolescent cannabis users [adjusted odds ratio (ORadj) = 1.74; 95% confidence interval (CI) 1.10-2.75] and those who reported repeated disruptive behaviours (ORadj = 1.71; 95% CI 1.15-2.55) or persistent common mental disorders in adolescence (ORadj = 1.60; 95% CI 1.07-2.40). Similar associations were present when participants with children were included in the same category as those in employment, education, or training. CONCLUSIONS: Young people with an early onset of mental health and behavioural problems are at risk of failing to make the transition from school to employment. This finding reinforces the importance of integrated employment and mental health support programmes.

The association between higher maternal pre-pregnancy body mass index and increased birth weight, adiposity and inflammation in the newborn.

BACKGROUND: Excess adiposity and adiposity-related inflammation are known risk factors for cardiovascular disease in adults; however, little is known regarding the determinants of adiposity-related inflammation at birth. OBJECTIVES: The aim of this study was to investigate the association between maternal pre-pregnancy BMI and newborn adiposity and inflammation. METHODS: Paired maternal (28-week gestation) and infant (umbilical cord) blood samples were collected from a population-derived birth cohort (Barwon Infant Study, n = 1074). Data on maternal comorbidities and infant birth anthropomorphic measures were compiled, and infant aortic intima-media thickness was measured by trans-abdominal ultrasound. In a selected subgroup of term infants (n = 161), matched maternal and cord lipids, high-sensitivity C-reactive protein (hsCRP) and maternal soluble CD14 were measured. Analysis was completed by using pairwise correlation and linear regression. Because of their non-normal distribution, pathology blood measures were log transformed prior to analysis. RESULTS: Maternal pre-pregnancy BMI was positively associated with increased birth weight (mean difference 17.8 g per kg m-2 , 95% CI 6.6 to 28.9; p = 0.002), newborn mean skin-fold thickness (mean difference 0.1 mm per kg m-2 , 95% CI 0.0 to 0.1; p < 0.001) and cord blood hsCRP (mean difference of 4.2% increase in hsCRP per kg m-2 increase in pre-pregnancy BMI, 95% CI 0.6 to 7.7%, p = 0.02), but not cord blood soluble CD14. Inclusion of maternal hsCRP as a covariate attenuated the associations between pre-pregnancy BMI and both newborn skin-fold thickness and cord blood hsCRP. CONCLUSION: Higher maternal pre-pregnancy BMI is associated with increased newborn adiposity and inflammation. These associations may be partially mediated by maternal inflammation during pregnancy.

Symptom covariance accounts for behavioral approach associations across impulse control disorders.

Behavioral approach system (BAS) dysfunction has been identified as a correlate of and a potential mechanism for attention-deficit/hyperactivity disorder (ADHD) and comorbid disorders. This study examined the role of symptom covariation in the relations among BAS dysfunction, ADHD symptoms, and comorbid impulsive personality disorder features. Undergraduates (N = 207) completed measures of BAS functioning, ADHD symptoms, and borderline and antisocial personality disorder symptoms, and associated features (i.e., relational aggression). Hierarchical regression suggested that age, impulsive ADHD symptoms, and relational aggression were associated with BAS functioning. Adding other ADHD symptom dimensions (inattention, hyperactivity) and antisocial and borderline scores to the model did not increase variance accounted for beyond that accounted for by ADHD impulsivity scores. Results highlight a role of symptom covariance in the previously demonstrated relation between BAS, impulsive presentations of ADHD, and comorbid impulsive personality pathology. Implications for etiological models of ADHD and its co-occurrence with other disorders are discussed.

Mindfulness programming for parents and teachers of children with ADHD.

BACKGROUND: Parents and teachers of children with attention-deficit/hyperactivity disorder (ADHD) are at-risk for a range of suboptimal psychosocial outcomes, including mental health difficulties and heightened stress, problems perhaps ameliorated through mindfulness-based programming. OBJECTIVE: To show pilot data from an investigation of the outcomes of a purpose-built mindfulness training for parents and teachers of children with ADHD (N = 26). METHODS: The program represents a purpose-driven modification of the Mindfulness-Based Stress Reduction (MBSR) curriculum. Namely, we reduced participant time commitment and added psychoeducation about ADHD with brief parent training. The measurement protocol included measures of stress, anxiety, depression, and mindfulness. RESULTS: Following the 8-week program, parents and teachers reported reduced perceived stress, reduced self-reported anxiety, and improvements in some facets of mindfulness. CONCLUSION: The work highlights the promise of specialized mindfulness-based interventions in promoting positive psychosocial outcomes in specific at-risk groups, such as the carers of children with ADHD.

Vitamin D insufficiency in the first 6 months of infancy and challenge-proven IgE-mediated food allergy at 1 year of age: a case-cohort study.

BACKGROUND: Ecological evidence suggests vitamin D insufficiency (VDI) due to lower ambient ultraviolet radiation (UVR) exposure may be a risk factor for IgE-mediated food allergy. However, there are no studies relating directly measured VDI during early infancy to subsequent challenge-proven food allergy. OBJECTIVE: To prospectively investigate the association between VDI during infancy and challenge-proven food allergy at 1 year. METHODS: In a birth cohort (n = 1074), we used a case-cohort design to compare 25-hydroxyvitamin D3 (25(OH)D3 ) levels among infants with food allergy vs a random subcohort (n = 274). The primary exposures were VDI (25(OH)D3 <50 nM) at birth and 6 months of age. Ambient UVR and time in the sun were combined to estimate UVR exposure dose. IgE-mediated food allergy status at 1 year was determined by formal challenge. Binomial regression was used to examine associations between VDI, UVR exposure dose and food allergy and investigate potential confounding. RESULTS: Within the random subcohort, VDI was present in 45% (105/233) of newborns and 24% (55/227) of infants at 6 months. Food allergy prevalence at 1 year was 7.7% (61/786), and 6.5% (53/808) were egg-allergic. There was no evidence of an association between VDI at either birth (aRR 1.25, 95% CI 0.70-2.22) or 6 months (aRR 0.93, 95% CI 0.41-2.14) and food allergy at 1 year. CONCLUSIONS: There was no evidence that VDI during the first 6 months of infancy is a risk factor for food allergy at 1 year of age. These findings primarily relate to egg allergy, and larger studies are required.

Association Between Pubertal Onset and Symptoms of ADHD in Female University Students.

OBJECTIVE: This exploratory study investigated how the timing of female pubertal maturation was associated with the symptoms of ADHD in a non-clinical female undergraduate sample (N = 253). METHOD: Participants (Mage = 20.2 ± 1.7 years) completed a set of self-report rating scales examining pubertal onset and ADHD symptoms and related deficits. RESULTS: Logistic regression analysis indicated that early puberty was associated with elevation in symptoms, including difficulties in attention (odds ratio [OR] = 1.270, p = .019), emotion regulation (OR = 1.070, p = .038), and more risky behavior (OR = 1.035, p = .045). That is, increased symptom endorsement was shown to significantly help classify those who reported having an earlier pubertal onset relative to their peers. CONCLUSION: Findings highlight the potential role of sex hormones during puberty in explaining the gender differences in prevalence rates of ADHD and symptom profiles.

Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies.

The effect of a tunable, externally coupled Fabry-Perot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this Letter. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example, by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high-electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-Perot cavity, are presented and discussed. Tuning the externally coupled Fabry-Perot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence, and magnetic field direction and strength.

Effects of school-based interventions for direct delivery of physical activity on fitness and cardiometabolic markers in children and adolescents: a systematic review of randomized controlled trials.

UNLABELLED: To evaluate the effectiveness of school-based physical activity interventions on fitness, adiposity and cardiometabolic outcomes among schoolchildren. Medline, Embase, EBSCOhost CINAHL and ERIC databases were searched up to October 2012. INCLUSION CRITERIA: intervention delivered at school with controls having no intervention or usual physical education classes; participants aged 5-18 years; outcomes spanning some or all of the above. We assessed levels of evidence for identified trials based on methodological quality and sample size. Dose of the interventions (a total summary measure of intensity, frequency and duration) were considered. Eighteen randomized controlled trials (RCTs, total participants = 6,207) were included, of which six were large, higher quality trials with high dose of the intervention. The intervention was consistent in increasing fitness with large, higher quality studies and high dose of intervention providing strong evidence. Dose of school-based physical activity is an important determinant of trial efficiency. Some large, higher quality RCTs provided strong evidence for interventions to decrease skin-fold thickness, increase fitness and high-density lipoprotein cholesterol. Evidence for body mass index, body fat and waist circumference, blood pressure and triglycerides, low-density lipoprotein cholesterol and total cholesterol remain inconclusive and require additional higher quality studies with high dose of interventions to provide conclusive evidence.

Planum temporale morphology in children with developmental dyslexia.

The planum temporale is a highly lateralized cortical region, located within Wernicke's area, which is thought to be involved in auditory processing, phonological processing, and language. Research has linked abnormal morphology of the planum temporale to developmental dyslexia, although results have varied in large part due to methodological inconsistencies in the literature. This study examined the asymmetry of the planum temporale in 29 children who met criteria for dyslexia and 26 children whose reading was unimpaired. Leftward asymmetry of the planum temporale was found in the total sample and this leftward asymmetry was significantly reduced in children with dyslexia. This reduced leftward asymmetry in children with dyslexia was due to a planum temporale that is larger in the right hemisphere. This study lends support to the idea that planum temporale asymmetry is altered in children with developmental dyslexia.

Are cognitive control and stimulus-driven processes differentially linked to inattention and hyperactivity in preschoolers?

Temperament and attention-deficit/hyperactivity disorder (ADHD) are both typically viewed as biologically based behavioural constructs. There is substantial overlap between ADHD symptoms and specific temperamental traits, such as effortful control, especially in young children. Recent work by Martel and colleagues ( 2009 , 2011 ) suggests that cognitive control temperamental processes are more closely related to inattention symptoms, whereas stimulus-driven temperamental processes are linked to hyperactivity-impulsivity. The present study tested a model of temperament and ADHD symptoms in typically developing preschoolers and those at risk for ADHD using structural equation modelling. Data were from larger study on ADHD in a short-term longitudinal sample with parent/teacher reports and neurocognitive testing. Participants included 214 preschool children (72.9% male) from diverse ethnic/racial backgrounds and a wide range of socioeconomic status from a large metropolitan center. Cognitive control processes, such as effortful control, but not stimulus-driven processes, are related to inattention and hyperactivity. In contrast, stimulus-driven processes, such as emotional reactivity, were related only to hyperactivity symptoms longitudinally. These results suggest that early temperament behaviours and cognitive processes may be indicators of later childhood behavioural difficulties with lasting consequences.

Morbidity patterns among the underweight, overweight and obese between 2 and 18 years: population-based cross-sectional analyses.

CONTEXT: No study has documented how symptomatic morbidity varies across the body mass index (BMI) spectrum (underweight, normal weight, overweight and obese) or across the entire child and adolescent age range. OBJECTIVE: To (1) quantify physical and psychosocial morbidities experienced by 2-18-year-olds according to BMI status and (2) explore morbidity patterns by age. DESIGN, SETTING AND PARTICIPANTS: Cross-sectional data from two Australian population studies (the Longitudinal Study of Australian Children and the Health of Young Victorians Study) were collected during 2000-2006. Participants were grouped into five age bands: 2-3 (n=4606), 4-5 (n=4983), 6-7 (n=4464), 8-12 (n=1541) and 13-18 (n=928) years. MAIN MEASURES: Outcomes-Parent- and self-reported global health; physical, psychosocial and mental health; special health-care needs; wheeze; asthma and sleep problems. Exposure-measured BMI (kg m(-2)) categorised using standard international cutpoints. ANALYSES: The variation in comorbidities across BMI categories within and between age bands was examined using linear and logistic regression models. RESULTS: Comorbidities varied with BMI category for all except sleep problems, generally showing the highest levels for the obese category. However, patterns differed markedly between age groups. In particular, poorer global health and special health-care needs were associated with underweight in young children, but obesity in older children. Prevalence of poorer physical health varied little by BMI in 2-5-year-olds, but from 6 to 7 years was increasingly associated with obesity. Normal-weight children tended to experience the best psychosocial and mental health, with little evidence that the U-shaped associations of these variables with BMI status varied by age. Wheeze and asthma increased slightly with BMI at all ages. CONCLUSIONS: Deviation from normal weight is associated with health differences in children and adolescents that vary by morbidity and age. As well as lowering risks for later disease, promoting normal body weight appears central to improving the health and well-being of the young.

Near-infrared characterization of gallium nitride photonic-crystal waveguides and cavities.

We report the design and optical characterization of fully suspended wire waveguides and photonic crystal (PhC) membranes fabricated on a gallium nitride layer grown on silicon substrate operating at 1.5 µm. W1-type PhC waveguides are coupled with suspended wires and are investigated using a standard end-fire setup. The experimental and theoretical dispersion properties of the propagating modes in the wires and photonic-crystal waveguides are shown. Modified L3 cavities with quality factors of up to 2200 and heterostructure cavities with quality factors of up to 5400 are experimentally demonstrated.