Ex situ Ge-doping of CZTS nanocrystals and CZTSSe solar absorber films

Cu₂ZnSn(S,Se)₄ (CZTSSe) is a promising material for thin-film photovoltaics, however, the open-circuit voltage (V_OC) deficit of CZTSSe prevents the device performance from exceeding 13% conversion efficiency. CZTSSe is a heavily compensated material that is rich in point defects and prone to the formation of secondary phases. The landscape of these defects is complex and some mitigation is possible by employing non-stoichiometric conditions. Another route used to reduce the effects of undesirable defects is the doping and alloying of the material to suppress certain defects and improve crystallization, such as with germanium. The majority of works deposit Ge adjacent to a stacked metallic precursor deposited by physical vapour deposition before annealing in a selenium rich atmosphere. Here, we use an established hot-injection process to synthesise Cu₂ZnSnS₄ nanocrystals of a pre-determined composition, which are subsequently doped with Ge during selenisation to aid recrystallisation and reduce the effects of Sn species. Through Ge incorporation, we demonstrate structural changes with a negligible change in the energy bandgap but substantial increases in the crystallinity and grain morphology, which are associated with a Ge-Se growth mechanism, and gains in both the V_OC and conversion efficiency. We use surface energy-filtered photoelectron emission microscopy (EF-PEEM) to map the surface work function terrains and show an improved electronic landscape, which we attribute to a reduction in the segregation of low local effective work function (LEWF) Sn(II) chalcogenide phases.

Graphene-diamond junction photoemission microscopy and electronic interactions

Polycrystalline graphene was transferred onto differently terminated epitaxial layers of boron-doped diamond deposited onto single crystal substrates. Chemical and electronic characterisation was performed using energy-filtered photoemission electron microscopy and angle-resolved photoemission spectroscopy. Electronic interaction between the diamond and graphene was observed, where doping of the graphene on the hydrogen and oxygen terminated diamond was n-doping of 250 meV and 0 meV respectively. We found that the wide window of achievable graphene doping is effectively determined by the diamond surface dipole, easily tuneable with a varying surface functionalisation. A Schottky junction using the graphene-diamond structure was clearly observed and shown to reduce downward band bending of the hydrogen terminated diamond, producing a Schottky barrier height of 330 meV.

Correlating Thermionic Emission with Specific Surface Reconstructions in a <100> Hydrogenated Single-Crystal Diamond

Thermionic emission relies on the low work function and negative electron affinity of the, often functionalized, surface of the emitting material. However, there is little understanding of the interplay between thermionic emission and temperature-driven dynamic surface transformation processes as these are not represented on the traditional Richardson-Dushman equation for thermionic emission. Here, we show a new model for thermionic emission that can reproduce the effect of dynamic surface changes on the electron emission and correlate the components of the thermionic emission with specific surface reconstruction phases on the surface of the emitter. We use hydrogenated <100> single-crystal and polycrystalline diamonds as thermionic emitters to validate our model, which shows excellent agreement with the experimental data and could be applicable to other emitting materials. Furthermore, we find that tailoring the coverage of specific structures of the C(100)-(2 × 1):H surface reconstruction could increase the thermionic emission of diamond by several orders of magnitude.

Anodization study of epitaxial graphene: insights on the oxygen evolution reaction of graphitic materials

The photoemission electron microscopy and x-ray photoemission spectroscopy were utilized for the study of anodized epitaxial graphene (EG) on silicon carbide as a fundamental aspect of the oxygen evolution reaction on graphitic materials. The high-resolution analysis of surface morphology and composition quantified the material transformation during the anodization. We investigated the surface with lateral resolution <150 nm, revealing significant transformations on the EG and the role of multilayer edges in increasing the film capacitance.

Characterisation of thermionic emission current with a laser-heated system

Thermionic emitting materials are relevant for several technological applications like electron guns, X-ray sources, or thermionic energy converters. As new materials and surface functionalisations that enable thermionic emission are developed, it is essential to be able to test them in a repeatable and reliable manner. Here, we present a CO₂ laser-heated system for thermionic tests that can be used to test the thermionic emission current of different materials regardless of the optical properties or form factor. Our system can reach sample temperatures of T ≈ 1000 °C and can follow pre-programmed heating profiles. Additionally, a double thermo-electrical decoupling provides a very low electrical noise environment while keeping the sample heat loss to a minimum. Experimental data on sample temperature and thermionic current from a hydrogen terminated single crystal diamond are presented and discussed.

Frontal alpha asymmetry moderates the relations between behavioral inhibition and social-effect ERN

Behavioral inhibition (BI) is an early temperamental precursor of anxiety disorders, characterized by withdrawal from novel situations. Some but not all young children with BI go on to display anxiety disorders. Neural correlates, such as frontal alpha asymmetry or event-related negativity (ERN), could moderate the relations between early BI and later anxiety. The goal of this longitudinal study was to test frontal alpha asymmetry as a potential moderator of the relation between BI and later anxiety, and of the relation between BI and the social-effect ERN. 100 children were assessed for BI at ages 2 and 3, and we collected EEG during resting state and the social Flanker task at age 12. Frontal alpha asymmetry did not correlate with BI or anxiety, nor did it moderate the relation between early BI and later anxiety. However, frontal alpha asymmetry did moderate the relation between BI and the social-effect ERN. This suggests that, in adolescents who previously manifested BI, a pattern of resting EEG associated with avoidance predicts hypersensitivity to errors in a social context.

Early-childhood social reticence predicts SCR-BOLD coupling during fear extinction recall in preadolescent youth

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Threat circuit function may develop differently in children with different temperamental profiles, such as high vs. low social reticence.

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We relate individual differences in longitudinally assessed, observed socially reticent behavior to brain-physiology interactions during extinction recall.

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Childhood social reticence predicts a distinct pattern of hemodynamic-autonomic covariation when recalling extinguished threat and safety cues.

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Covariation patterns indicated that socially reticent youth had difficulty tracking safety as a function of stimulus resemblance to the safe stimulus.

Social Reticence (SR) is a temperament construct identified in early childhood that is expressed as shy, anxiously avoidant behavior and, particularly when stable, robustly associated with risk for anxiety disorders. Threat circuit function may develop differently for children high on SR than low on SR. We compared brain function and behavior during extinction recall in a sample of 11-to-15-year-old children characterized in early childhood on a continuum of SR. Three weeks after undergoing fear conditioning and extinction, participants completed a functional magnetic resonance imaging extinction recall task assessing memory and threat differentiation for conditioned stimuli. Whereas self-report and psychophysiological measures of differential conditioning, extinction, and extinction recall were largely similar across participants, SR-related differences in brain function emerged during extinction recall. Specifically, childhood SR was associated with a distinct pattern of hemodynamic-autonomic covariation in the brain when recalling extinguished threat and safety cues. SR and attention focus impacted associations between trial-by-trial variation in autonomic responding and in brain activation. These interactions occurred in three main brain areas: the anterior insular cortex (AIC), the anterior subdivision of the medial cingulate cortex (aMCC), and the dorsolateral prefrontal cortex (dlPFC). This pattern of SCR-BOLD coupling may reflect selective difficulty tracking safety in a temperamentally at-risk population.

Mapping Shunting Paths at the Surface of Cu2ZnSn(S,Se)4 Films via Energy-Filtered Photoemission Microscopy

The performance of Cu₂ZnSn(S,Se)₄ thin-film solar cells, commonly referred to as kesterite or CZTSSe, is limited by open-circuit voltage (V_OC) values less than 60% of the maximum theoretical limit. In the present study, we employ energy-filtered photoemission microscopy to visualize nanoscale shunting paths in solution-processed CZTSSe films, which limit the V_OC of cells to approximately 400 mV. These studies unveil areas of local effective work function (LEWF) narrowly distributed around 4.9 eV, whereas other portions show hotspots with LEWF as low as 4.2 eV. Localized valence band spectra and density functional theory calculations allow rationalizing the LEWF maps in terms of the CZTSSe effective work function broadened by potential energy fluctuations and nanoscale Sn(S,Se) phases.

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Exploring Cu₂ZnSn(S,Se)₄ films with energy-filtered photoelectron emission microscopy

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Sub-micrometer hotspots of low effective work function are revealed

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Valence band spectra of hotspots suggests discrete Sn(S,Se) surface domains

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Sn(S,Se) domains may act as carrier shunts in PV devices

A theoretical study of substitutional boron-nitrogen clusters in diamond

Substitutional clusters of multiple light element dopants are a promising route to the elusive shallow donor in diamond. To understand the behaviour of co-dopants, this report presents an extensive first principles study of possible clusters of boron and nitrogen. We use periodic hybrid density functional calculations to predict the geometry, stability and electronic excitation energies of a range of clusters containing up to five N and/or B atoms. Excitation energies from hybrid calculations are compared to those from the empirical marker method, and are in good agreement. When a boron-rich or nitrogen-rich cluster consists of three to five atoms, the minority dopant element-a nitrogen or boron atom respectively-can be in either a central or peripheral position. We find B-rich clusters are most stable when N sits centrally, whereas N-rich clusters are most stable with B in a peripheral position. In the former case, excitation energies mimic those of the single boron acceptor, while the latter produce deep levels in the band-gap. Implications for probable clusters that would arise in high-pressure high-temperature co-doped diamond and their properties are discussed.

Time-frequency approaches to investigating changes in feedback processing during childhood and adolescence

Processing feedback from the environment is an essential function during development to adapt behavior in advantageous ways. One measure of feedback processing, the feedback negativity (FN), is an ERP observed following the presentation of feedback. Findings detailing developmental changes in the FN have been mixed, possibly due to limitations in traditional ERP measurement methods. Recent work shows that both theta and delta frequency activity contribute to the FN; utilizing time-frequency methods to measure change in power and phase in these frequency bands may provide more accurate representation of feedback processing development in childhood and adolescence. We employ time-frequency power and intertrial phase synchrony measures, in addition to conventional time-domain ERP methods, to examine the development of feedback processing in the theta (4-7 Hz) and delta (.1-3 Hz) bands throughout adolescence. A sample of 54 female participants (8-17 years old) completed a gambling task while EEG was recorded. As expected, time-domain ERP amplitudes showed no association with age. In contrast, significant effects were observed for the time-frequency measures, with theta power decreasing with age and delta power increasing with age. For intertrial phase synchrony, delta synchrony increased with age, while age-related changes in theta synchrony differed for gains and losses. Collectively, these findings highlight the importance of considering time-frequency dynamics when exploring how the processing of feedback develops through late childhood and adolescence. In particular, the role of delta band activity and theta synchrony appear central to understanding age-related changes in the neural response to feedback.

A Perspective on the Application of Spatially Resolved ARPES for 2D Materials

In this paper, a perspective on the application of Spatially- and Angle-Resolved PhotoEmission Spectroscopy (ARPES) for the study of two-dimensional (2D) materials is presented. ARPES allows the direct measurement of the electronic band structure of materials generating extremely useful insights into their electronic properties. The possibility to apply this technique to 2D materials is of paramount importance because these ultrathin layers are considered fundamental for future electronic, photonic and spintronic devices. In this review an overview of the technical aspects of spatially localized ARPES is given along with a description of the most advanced setups for laboratory and synchrotron-based equipment. This technique is sensitive to the lateral dimensions of the sample. Therefore, a discussion on the preparation methods of 2D material is presented. Some of the most interesting results obtained by ARPES are reported in three sections including: graphene, transition metal dichalcogenides (TMDCs) and 2D heterostructures. Graphene has played a key role in ARPES studies because it inspired the use of this technique with other 2D materials. TMDCs are presented for their peculiar transport, optical and spin properties. Finally, the section featuring heterostructures highlights a future direction for research into 2D material structures.

Imaging the Predicted Isomerism of Oligo(aniline)s: A Scanning Tunneling Microscopy Study

The self-assembly of two emeraldine base tetra(aniline) derivatives is investigated using scanning tunneling microscopy. A combination of the scanning tunneling microscopy data and calculations reveals the presence of predicted cis/trans isomerism in this oxidation state. This isomerism is shown to hinder self-assembly into ordered structures, and provides indications as to why the properties of these materials, and their parent polymer, polyaniline, remain unfulfilled.

Perturbed threat monitoring following a traumatic event predicts risk for post-traumatic stress disorder

BACKGROUND

Post-traumatic stress disorder (PTSD) is a chronic and difficult to treat psychiatric disorder. Objective, performance-based diagnostic markers that uniquely index risk for PTSD above and beyond subjective self-report markers could inform attempts to improve prevention and early intervention. We evaluated the predictive value of threat-related attention bias measured immediately after a potentially traumatic event, as a risk marker for PTSD at a 3-month follow-up. We measured the predictive contribution of attentional threat bias above and beyond that of the more established marker of risk for PTSD, self-reported psychological dissociation.

METHOD

Dissociation symptoms and threat-related attention bias were measured in 577 motor vehicle accident (MVA) survivors (mean age = 35.02 years, 356 males) within 24 h of admission to an emergency department (ED) of a large urban hospital. PTSD symptoms were assessed at a 3-month follow-up using the Clinician-Administered PTSD Scale (CAPS).

RESULTS

Self-reported dissociation symptoms significantly accounted for 16% of the variance in PTSD at follow-up, and attention bias toward threat significantly accounted for an additional 4% of the variance in PTSD.

CONCLUSIONS

Threat-related attention bias can be reliably measured in the context of a hospital ED and significantly predicts risk for later PTSD. Possible mechanisms underlying the association between threat bias following a potentially traumatic event and risk for PTSD are discussed. The potential application of an attention bias modification treatment (ABMT) tailored to reduce risk for PTSD is suggested.

Frequency and topography in monkey electroencephalogram during action observation: possible neural correlates of the mirror neuron system

The observation of actions executed by others results in desynchronization of electroencephalogram (EEG) in the alpha and beta frequency bands recorded from the central regions in humans. On the other hand, mirror neurons, which are thought to be responsible for this effect, have been studied only in macaque monkeys, using single-cell recordings. Here, as a first step in a research programme aimed at understanding the parallels between human and monkey mirror neuron systems (MNS), we recorded EEG from the scalp of two monkeys during action observation. The monkeys were trained to fixate on the face of a human agent and subsequently to fixate on a target upon which the agent performed a grasping action. We found that action observation produced desynchronization in the 19-25 Hz band that was strongest over anterior and central electrodes. These results are in line with human data showing that specific frequency bands within the power spectrum of the ongoing EEG may be modulated by observation of actions and therefore might be a specific marker of MNS activity.

Impact of negative affectively charged stimuli and response style on cognitive-control-related neural activation: an ERP study

The canonical AX-CPT task measures two forms of cognitive control: sustained goal-oriented control ("proactive" control) and transient changes in cognitive control following unexpected events ("reactive" control). We modified this task by adding negative and neutral International Affective Picture System (IAPS) pictures to assess the effects of negative emotion on these two forms of cognitive control. Proactive and reactive control styles were assessed based on measures of behavior and electrophysiology, including the N2 event-related potential component and source space activation (Low Resolution Tomography [LORETA]). We found slower reaction-times and greater DLPFC activation for negative relative to neutral stimuli. Additionally, we found that a proactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during actively maintained previously cued information and that a reactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during just-in-time environmentally triggered information. This pattern of results was evident in relatively neutral contexts, but in the face of negative emotion, these associations were not found, suggesting potential response style-by-emotion interaction effects on prefrontal neural activation.

Early childhood temperament predicts substance use in young adults

Behavioral inhibition (BI) is an important early childhood marker of risk for later psychiatric problems. The current 20-year prospective, longitudinal study focused on individual differences in this early temperament and adolescent brain function. As adolescents, 83 participants initially identified in infancy with the temperament of BI were assessed using functional imaging to examine striatal responses to incentives. Five years later, as young adults, these participants provided self-report of their substance use. Our findings show that children's early temperament interacts with their striatal sensitivity to incentives in adolescence to predict their level of substance use in young adulthood. Those young adults who, as children, showed the highest levels of BI reported the greatest substance use if, as adolescents, they also exhibited striatal hypersensitivity to incentives. These longitudinal data delineate one developmental pathway involving early biology and brain mechanisms for substance use in young adulthood.

Telomere length and early severe social deprivation: linking early adversity and cellular aging

Accelerated telomere length attrition has been associated with psychological stress and early adversity in adults; however, no studies have examined whether telomere length in childhood is associated with early experiences. The Bucharest Early Intervention Project is a unique randomized controlled trial of foster care placement compared with continued care in institutions. As a result of the study design, participants were exposed to a quantified range of time in institutional care, and represented an ideal population in which to examine the association between a specific early adversity, institutional care and telomere length. We examined the association between average relative telomere length, telomere repeat copy number to single gene copy number (T/S) ratio and exposure to institutional care quantified as the percent of time at baseline (mean age 22 months) and at 54 months of age that each child lived in the institution. A significant negative correlation between T/S ratio and percentage of time was observed. Children with greater exposure to institutional care had significantly shorter relative telomere length in middle childhood. Gender modified this main effect. The percentage of time in institutional care at baseline significantly predicted telomere length in females, whereas the percentage of institutional care at 54 months was strongly predictive of telomere length in males. This is the first study to demonstrate an association between telomere length and institutionalization, the first study to find an association between adversity and telomere length in children, and contributes to the growing literature linking telomere length and early adversity.

Attention bias away from threat during life threatening danger predicts PTSD symptoms at one-year follow-up

BACKGROUND

Recent studies find a correlation between attentional threat avoidance under stress and posttraumatic stress symptoms. In this study, we assessed this association longitudinally in exposed and unexposed individuals. The degree of threat avoidance during exposure was expected to predict levels of posttraumatic stress symptoms 1 year later.

METHODS

Thirty-two participants were recruited and followed for 12 months, including 18 subjects exposed to rocket attacks and 14 nonexposed subjects. At 1-year follow-up, participants completed self-reports and an attention dot-probe task assessing threat-related bias.

RESULTS

State anxiety decreased at follow-up in exposed participants, though posttraumatic stress disorder (PTSD) and depression symptoms remained higher in exposed than in the nonexposed group. Attentional threat avoidance during imminent danger in the exposed group changed to threat attendance a year later, such that both the exposed and the nonexposed group exhibited similar threat bias patterns. As hypothesized, in the exposed group, stronger attentional threat avoidance during stress exposure predicted higher levels of PTSD symptoms 1 year later.

CONCLUSIONS

Attention bias away from threat during acute stress may relate to risk for PTSD. This suggests that neurocognitive measures may index risk for PTSD.

Electrochemical properties of two dimensional assemblies of insulating diamond particles

The electrochemical properties of two-dimensional assemblies of 500 nm type Ib diamond particles are investigated as a function of their surface oxidation state. High Pressure High Temperature particles are sequentially exposed to a hot strong acid bath and to H(2) plasma in order to generate oxygen (ODP) and hydrogen surface terminations (HDP). Changes in the surface composition following the chemical treatments are confirmed by FTIR. Electrophoretic mobility measurements show that the diamond particles exhibit a negative surface charge at pH above 7 independently of the surface termination. Oxidation in the acid bath and subsequent reduction in the H(2) plasma only affects about 30% of the particle surface charge. The intrinsic negative charge allows the formation of 2D assemblies by electrostatic adsorption on poly(diallyldimethylammonium chloride) (PDADMAC) modified In-doped SnO(2) electrodes (ITO). The particle number density in the assembly was controlled by the adsorption time up to a maximum coverage of ca. 40%. Cyclic voltammetry in the absence of redox species in solution show that the acid treatment effectively removes responses associated with sp(2) carbon impurities, resulting in a potential independent capacitive signal. On the other hand, HDP assemblies are characterized by a charging process at a potential above 0.1 V vs Ag/AgCl. These responses are associated with hole-injection into the valence band edge which is shifted to approximately -4.75 eV vs vacuum upon hydrogenation. Information concerning the position of the valence band edge as well as hole number density at the HDP surface as a function of the applied potential are extracted from the electrochemical analysis.

Experimental and Modeling Studies of B Atom Number Density Distributions in Hot Filament Activated B2H6/H2 and B2H6/CH4/H2 Gas Mixtures

Experimental and modeling studies of the gas-phase chemistry occurring in dilute, hot filament (HF) activated B2H6/H2 and B2H6/CH4/H2 gas mixtures are reported. Spatially resolved relative number densities of B (and H) atoms have been measured by resonance enhanced multiphoton ionization methods, as a function of process conditions (e.g. the HF material and its temperature, the B2H6/H2 mixing ratio, and the presence (or not) of added CH4). Three-dimensional modeling of the H/B chemistry prevailing in such HF activated gas mixtures using a simplified representation of the gas phase chemistry succeeds in reproducing all of the experimentally observed trends, and in illustrating the key role of the "H-shifting" reactions BHx + H <= => BHx-1 + H2 (x = 1-3) in enabling rapid interconversion between the various BHx (x = 0-3) species. CH4 addition, at partial pressures appropriate for growth of boron-doped diamond by chemical vapor deposition methods, leads to approximately 30% reduction in the measured B atom signal near the HF. The modeling suggests that this is mainly due to concomitant H atom depletion near the HF, but it also allows us a first assessment of the possible contributions from B/C coupling reactions upon CH4 addition to HF activated B2H6/H2 gas mixtures.

Measuring failure of orthodontic treatment: a comparison of outcome indicators

OBJECTIVE

To compare treatment failure rates on a sample of completed and discontinued orthodontic treatment cases as measured by PAR, IOTN and ICON to determine whether the use of a sole index would suffice.

SUBJECTS AND METHOD

All patients completing or discontinuing orthodontic treatment in the hospital orthodontic departments in the Northern Region during two calendar months were identified and pre and post-treatment models were analysed. PAR scores, IOTN (DHC and AC) and ICON were recorded.

RESULTS

One-hundred-and-forty-five cases were identified and 15 had incomplete records on the day of analysis. The final sample was therefore 130. The overall treatment discontinuation rate of these 130 patients was 24.6%. The treatment failure rate with respect to occlusal improvement varied from 3.1% when measured by PAR and 10.0% using ICON. With respect to residual need it varied from 0.77 to 20.1% with respect to IOTN depending on the criteria examined. The residual treatment need with respect to ICON was 17.2%.

CONCLUSIONS

Different occlusal indices give differing failure rates when used on the same patients with ICON being the most critical index. We felt that ICON was the most valid with respect to identifying treatment failure. Its use would enable international comparison of results.

A comparison of the index of complexity outcome and need (ICON) with the peer assessment rating (PAR) and the index of orthodontic treatment need (IOTN)

AIM

To evaluate any relationship between ICON, IOTN and PAR. To establish whether or not ICON could replace these indices as a measure of orthodontic treatment complexity, outcome and need.

METHOD

The study models of 55 consecutively treated cases were examined and PAR, IOTN and ICON recorded.

RESULTS

The study showed significant correlations between IOTN and ICON with respect to need and PAR and ICON with respect to outcome.

CONCLUSION

It appears that ICON does reflect UK opinion and the current study provides some evidence that ICON may effectively replace PAR and IOTN as a means of determining need and outcome.

The long-term benefits of orthodontic treatment

OBJECTIVE

This study aimed to evaluate post-treatment changes at least five years out of retention in a cohort of 100 consecutively started patients treated by a postgraduate student in a UK orthodontic department.

DESIGN

Analysis of study models using recognised occlusal indices. Setting Patients initially treated at Newcastle Dental Hospital were recalled for record collection.

MATERIALS AND METHODS

Study models and clinical photographs were taken for each patient attending for post-retention records. Weighted Peer Assessment Rating (PAR) Index and Index of Orthodontic Treatment Need (IOTN) scores were recorded for cases at the beginning, end and at least 5 years post-retention. Main outcome measures Post-treatment changes were evaluated using PAR Index and IOTN to evaluate extent and likelihood of change and to compare treatment modalities.

RESULTS

Seventy-eight patients attended for post-retention records. Overall PAR reduction immediately post-treatment was 68.6% and at a mean of 6.5 years post-retention was 55.5%. Dual arch fixed appliance treatments achieved the greatest reduction in PAR score, and maintained the reduction beyond the retention period better than other treatment modalities. Eighty-four per cent of the cohort still had some demonstrable improvement after a mean of 6.5 years post-retention. There was a residual need for treatment in 8% of cases on aesthetic grounds and in 24% of cases on dental health grounds.

CONCLUSIONS

Occlusal deterioration after orthodontic treatment is almost universal. Dual arch fixed appliance treatment provides the best post-treatment and post-retention result.

Violence exposure among school-age children in foster care: relationship to distress symptoms

OBJECTIVE

To describe the amount and nature of violence exposure and examine the relationship between violence exposure and distress symptoms among children in foster care.

METHOD

Violence exposure and distress symptoms were evaluated in interviews, conducted between July 1996 and March 1998, of 300 children from Los Angeles County living in out-of-home placement.

RESULTS

Interviews were successfully completed in 91% of eligible children. The majority of children (85%) reported having been a witness to violence, and 51% had been a victim of violence during their lifetime. Of these youths, 54% and 41%, respectively, reported having been exposed to such violence in the past 6 months. Girls, victims of assaultive violence and weapon related violence, and those reporting exposure to mild violence were more likely (p < .05) to have higher levels of distress symptoms than those without such characteristics, after age was controlled for.

CONCLUSIONS

Children in foster care continue to have high levels of violence exposure, even after removal from their biological parents' home. The relationship between violence exposure and distress symptoms underscores the need for clinicians to inquire about multiple forms of violence exposure among children living in out-of-home placement.

Association of DRD4 with attention problems in normal childhood development

Several previous studies found an association of clinically diagnosed attention deficit hyperactivity disorder with long alleles of a variation in the DRD4 dopamine receptor gene exon III coding sequence. We evaluated the DRD4 polymorphism in a non-clinically selected sample of children for whom maternal reports of attention problems were available at 4 and 7 years of age. There was a significant elevation in attention problem scores in children carrying DRD4 long alleles that accounted for 3-4% of total variation at each age and for 5-7% of the temporally stable component of the phenotype. Our results show that the DRD4 gene influences normal as well as pathological attention processes, and the results highlight the utility of longitudinal measurements in psychiatric genetics.

Temperamental contributions to social behavior: the moderating roles of frontal EEG asymmetry and gender

OBJECTIVES

Infant temperament is thought to provide one of the fundamental bases for social and emotional development. Few studies have examined the direct and indirect influences of early temperament and physiological disposition on later development.

METHOD

This article presents results of a longitudinal study that took place between the years 1989 and 1996 in which the relations between maternal reports of negative reactivity at 9 months of age and maternal ratings and laboratory observations of social wariness and sociability at 4 years of age (n = 97) were examined. Also examined were the moderating roles of (1) frontal electroencephalogram (EEG) asymmetry as assessed at 9 months of age and (2) the child's gender.

RESULTS

Negative reactivity predicted social wariness for infants with right frontal EEG asymmetry, but not for those with left frontal EEG asymmetry and for boys but not girls. The only significant predictor of sociability was gender. Specifically, at 4 years of age girls were rated higher on the measure of sociability than were boys.

CONCLUSION

The findings are discussed in terms of the roles of frontal EEG asymmetry and gender in moderating the impact of temperamental negative reactivity on later social behavior.

Continuity and discontinuity of behavioral inhibition and exuberance: psychophysiological and behavioral influences across the first four years of life

Four-month-old infants were screened (N = 433) for temperamental patterns thought to predict behavioral inhibition, including motor reactivity and the expression of negative affect. Those selected (N = 153) were assessed at multiple age points across the first 4 years of life for behavioral signs of inhibition as well as psychophysiological markers of frontal electroencephalogram (EEG) asymmetry. Four-month temperament was modestly predictive of behavioral inhibition over the first 2 years of life and of behavioral reticence at age 4. Those infants who remained continuously inhibited displayed right frontal EEG asymmetry as early as 9 months of age while those who changed from inhibited to noninhibited did not. Change in behavioral inhibition was related to experience of nonparental care. A second group of infants, selected at 4 months of age for patterns of behavior thought to predict temperamental exuberance, displayed a high degree of continuity over time in these behaviors.

Frontal electrocortical and cardiovascular reactivity during happiness and anger

The present study investigated electrocortical and cardiovascular reactivity during positive and negative emotion, and examined the relation of asymmetric frontal lobe activation to cardiovascular responses. Participants were 30 healthy, right-handed university students (mean age, 23.9; 60% female; 76% Caucasian). Electroencephalographic (EEG), blood pressure (BP), and heart rate (HR) responses were assessed while subjects engaged in laboratory tasks (personally-relevant recall tasks and film clips) designed to elicit happiness or anger. Happiness-inducing tasks evoked more prominent left than right frontal EEG activation, and greater left frontal EEG activation than anger-inducing tasks. However, anger-inducing tasks were, on average, associated with comparable left and right frontal EEG activation. Irrespective of emotional valence, cardiovascular activation was more pronounced during personally-relevant recall tasks than during the viewing of film clips. During anger recall, both greater left frontal EEG response (r=-0.46, P<0.02) and greater right frontal EEG response (r=-0.45, P<0.02) were correlated significantly with increased HR reactivity during the task. In addition, a right lateralized frontal EEG response during anger-inducing tasks was associated with greater concomitant systolic BP (P<0.03) and diastolic BP (P<0.008) reactivity. Exploratory analyses also indicated that men who displayed a left lateralized frontal EEG response during happiness-inducing tasks showed the greatest concomitant systolic BP and HR reactivity (P's<0.03). These findings suggest that asymmetric frontal EEG responses to emotional arousal may elicit different patterns of cardiovascular reactivity in healthy adults.

Developmental changes in heart period and high-frequency heart period variability from 4 months to 4 years of age

Cardiac measures of heart period and high-frequency heart period variability are increasingly employed as dependent variables in studies of social and emotional development in infancy and childhood. This study describes significant developmental increases in these measures in a longitudinal sample assessed at 4, 9, 14, 24, and 48 months of age. In addition, developmental changes in the characteristics of the heart period power spectra are described. These changes have implications for the quantification of high-frequency heart period variability in infancy and childhood. First, shorter analysis epoch lengths may be used for younger infants. Second, the commonly used high-frequency band for infants (0.24-1.04 Hz) appears to reach its practical limit at an age of around four years. Findings are discussed in relation to the design of developmental psychophysiological studies.

Stability and change of attachment at 14, 24, and 58 months of age: behavior, representation, and life events

Stability and change of attachment was examined longitudinally in a group of 48 children at 14, 24, and 58 months of age. Whereas attachment classifications showed stability between 14 and 24 months, lack of stability was the case between either 14 or 24 months and 58 months. Mothers of children who did not exhibit stability of attachment reported more negative and less positive life events. No correspondence was found between attachment classification at 14 or 24 months and mental representations at 58 months. However there was agreement between representational and behavioral measures of attachment at 58 months, where mental representations of attachment appeared to mirror and complement behavioral classification of the attachment relationship with the mother. Evidence for continuity of attachment from infancy to childhood internal representations was found only in a subgroup of children who showed stability of secure attachment between infancy and 58 months of age. These children exhibited greater Emotional Openness in the SAT at 4.5 years. Findings are discussed in terms of different positions in attachment theory and research regarding the stability and change of attachment relationships.

Preschool children's exposure to violence: relation of behavior problems to parent and child reports

A group of 155 parents and their preschool children attending Head Start reported on the children's exposure to community violence, level of distress symptoms, and behavioral problems. The behavioral correlates of exposure were found to differ according to exposure modality: internalizing problems were more likely in children who witnessed violence, and externalizing problems in those victimized by violence. Issues regarding self-reports by preschool children are highlighted, and clinical and research implications discussed.

The relations between temperament and empathy in 2-year-olds

The role of infant and toddler temperament in the prediction of empathy in 2-year-old children was examined. Assessments of temperament included reactivity and affect observed at 4 months of age, as well as inhibition at Age 2. Empathy was measured in 2-year-old children's responses to simulations of distress performed by their mothers and by an unfamiliar person. Children showed relatively more concern for the mother's distress, but they were also responsive to unfamiliar victims. Infants who were unreactive and showed little affect also showed less empathy toward the unfamiliar adult almost 2 years later. Inhibition toward an unfamiliar adult (but not toward the mother) at 2 years of age was negatively related to empathy. Inhibited temperament may thus have a major impact on young children's empathy in unfamiliar contexts. Findings also highlight the need to consider early underarousal as another dimension of temperament that may dampen expressions of empathic concern.

The relations between temperament and empathy in 2-year-olds

The role of infant and toddler temperament in the prediction of empathy in 2-year-old children was examined. Assessments of temperament included reactivity and affect observed at 4 months of age, as well as inhibition at Age 2. Empathy was measured in 2-year-old children's responses to simulations of distress performed by their mothers and by an unfamiliar person. Children showed relatively more concern for the mother's distress, but they were also responsive to unfamiliar victims. Infants who were unreactive and showed little affect also showed less empathy toward the unfamiliar adult almost 2 years later. Inhibition toward an unfamiliar adult (but not toward the mother) at 2 years of age was negatively related to empathy. Inhibited temperament may thus have a major impact on young children's empathy in unfamiliar contexts. Findings also highlight the need to consider early underarousal as another dimension of temperament that may dampen expressions of empathic concern.

Behavioral and psychophysiological correlates of self-presentation in temperamentally shy children

We examined temporal changes in behavior, regional brain electrical activity (EEG), heart rate, cardiac vagal tone, the startle eyeblink response, and salivary cortisol during a task designed to elicit self-presentation anxiety in a group of 7-year-olds, some of whom were classified as temperamentally shy. We found that temperamentally shy children displayed a significantly greater increase in anxious behavior, a greater increase in right, but not left, frontal EEG activity, and a greater increase in heart rate as the task became more demanding compared with their nonshy counterparts. However, the results failed to reveal any significant group differences on the startle eyeblink and salivary cortisol measures. The present findings extend our prior work, in which we found distinct patterns of psychophysiological activity on baseline measures, to differences on psychophysiological measures collected concurrently during a socially evaluative situation in temperamentally shy children.

Effects of acute prednisone administration on memory, attention and emotion in healthy human adults

We conducted a double-blind study in order to examine the effects of high doses of prednisone on memory, attention and emotion in humans. A total of 24 healthy undergraduate males self-administered either 160 mg of prednisone (n = 12) or a placebo (n = 12) for 4 consecutive days. We examined group differences in mood, regional brain electrical activity (EEG), the startle eyeblink response, memory recall and performance on an attention task after 4 days of treatment. We found significant group differences on measures of mood and frontal EEG alpha activity on 4-day treatment. Subjects treated with prednisone exhibited a significantly greater increase in self-reported negative emotion and greater relative right frontal EEG alpha activity on 4-day treatment compared with adults in the placebo group. We also found that subjects treated with prednisone recalled fewer objects on the memory task following treatment. No significant group differences were found on posterior EEG activity, the startle eyeblink measure, or the attention measure. These findings suggest that administration of high doses of exogenous prednisone may facilitate the experience of negative emotion and shifts in frontal EEG activity, and impair some aspects of cognitive functioning in humans. The multiple roles of glucocorticoids in memory, attention and emotion are discussed.

Temperament and regulation of emotion in the first years of life

Temperament is the tendency to express particular emotions with a certain intensity that is unique to each individual child. Although temperament seems to be biologically based, learning to regulate emotional expressions depends on caregiver input and socialization. Part of this process involves forming a trusting relationship with the infant so that he or she learns to rely on the parents to help "regulate" stressful or frustrating situations.

Music shifts frontal EEG in depressed adolescents

Recent studies have found that positive affect is associated with greater relative left frontal EEG activation and negative affect is associated with greater relative right frontal EEG activation. Further, chronically depressed adults typically display stable right frontal EEG activation. The present study investigated the effects of music on mood state and right frontal EEG activation associated with chronic depression. Fourteen chronically depressed female adolescents listened to rock music for a 23-minute session. These adolescents were compared with a control sample of chronically depressed female adolescents who were simply asked to sit and relax their minds and their muscles for the same time period. EEG was recorded during baseline, music, and postmusic for three minutes each, and saliva samples were collected before and after the session to determine the effects of the music on stress hormone (cortisol) levels. No group differences or changes were noted for observed or reported mood state. However, cortisol levels decreased and relative right frontal activation was significantly attenuated during and after the music procedure. It was concluded that music had positive effects on the physiological and biochemical measures even though observed and self-reported mood did not change.

Acoustic startle electromyographic (EMG) activity indexed from an electroculographic (EOG) electrode placement: a methodological note

Acoustic startle EMG responses were indexed from a traditional EOG electrode placement in 11 young adults while they viewed slides which varied in affective valence. We found, replicating earlier work that subjects' startle responses became more augmented as the content of the slides became more negative. The advantages of using an EOG electrode placement for measuring acoustic startle responses are discussed.

Fear-potentiated startle responses in temperamentally different human infants

Previous research has indicated that 4-month-old human infants who exhibit high degrees of motor activity and negative affect in response to the presentation of unfamiliar auditory and visual stimuli are likely to display behavioral inhibition as toddlers, while 4-month-old infants who display high degrees of motor activity and positive affect in response to the same stimuli are likely to be behaviorally exuberant toddlers. The present study examined baseline and fear-potentiated startle eyeblink responses during a stranger-approach paradigm at age 9 months in a group of infants, some of whom displayed high motor activity and negative affect and some of whom displayed high motor activity and positive affect at 4 months. The analyses revealed that the high motor/high negative group of infants exhibited a significantly greater increase in fear-potentiated startle amplitude at 9 months compared with the high motor/high positive group. There were no differences among groups of infants on baseline startle responses. These findings suggest that the origins of behavioral inhibition in early childhood may be linked to a low threshold for arousal in forebrain limbic areas.

Brief communication: a software solution for reducing startle eyeblink responses

We examined the viability of a software-based spectral method for reducing acoustic startle eyeblink responses. Fifteen young adults were presented with a 95 dB burst of white noise for 50 ms while they viewed slides that varied in affective valence. The startle EMG responses were analyzed using a discrete Fourier transform software-based spectral method. A significant linear trend was found between slide valence and startle amplitude, replicating previous work. Subjects' startle responses became more augmented as the content of the slides became more unpleasant. The advantages of software-based solutions for reducing startle EMG responses are discussed.

Individual differences in object permanence performance at 8 months: locomotor experience and brain electrical activity

This work was designed to investigate individual differences in hands-and-knees crawling and frontal brain electrical activity with respect to object permanence performance in 76 eight-month-old infants. Four groups of infants (one prelocomotor and 3 with varying lengths of hands-and-knees crawling experience) were tested on an object permanence scale in a research design similar to that used by Kermoian and Campos (1988). In addition, baseline EEG was recorded and used as an indicator of brain development, as in the Bell and Fox (1992) longitudinal study. Individual differences in frontal and occipital EEG power and in locomotor experience were associated with performance on the object permanence task. Infants successful at A-not-B exhibited greater frontal EEG power and greater occipital EEG power than unsuccessful infants. In contrast to Kermoian and Campos (1988), who noted that long-term crawling experience was associated with higher performance on an object permanence scale, infants in this study with any amount of hands and knees crawling experience performed at a higher level on the object permanence scale than prelocomotor infants. There was no interaction among brain electrical activity, locomotor experience, and object permanence performance. These data highlight the value of electrophysiological research and the need for a brain-behavior model of object permanence performance that incorporates both electrophysiological and behavioral factors.

EEG activation in 1-month-old infants of depressed mothers

Previous research has documented differences in the pattern of EEG activation between 3-month-old infants of depressed mothers and infants of nondepressed mothers. In the present study, EEG was recorded in even younger 1-month-old infants of depressed and nondepressed mothers. The infants of depressed mothers exhibited greater relative right frontal EEG asymmetry (due to reduced left frontal activation), and this pattern at 1 month was significantly related to 3-month EEG asymmetry. Right frontal EEG asymmetry was also related to more frequent negative facial expressions (sad and pre-cry faces) during the Brazelton exam. Finally, the infants of depressed mothers showed more indeterminate sleep, were less active, and cried less than infants of nondepressed mothers.

Factors affecting the outcome of orthodontic treatment within the general dental service

Previous studies have suggested large differences in the outcome of orthodontic treatment as measured by the PAR index in two adjacent regions of England. The aim of this prospective study was to identify any factors contributing to the mean PAR score reduction in the North Western region and the Mersey region. Forty-one practitioners submitted 375 sets of start models and 250 end of treatment models. The study ran for 36 months. There were no significant differences detected in the type of malocclusion treated or in outcome of treatment between the two regions with respect to the PAR and IOTN indices. This study did, however, clearly demonstrate that qualified orthodontic practitioners were achieving significantly better results with fixed appliances that practitioners with no orthodontic qualification who used fixed appliances.

Behavioral and neuroendocrine responses in shy children

Previous research has shown that infants who display a high frequency of motor activity and negative affect at 4 months of age are likely to be behaviorally inhibited toddlers. We examined social behaviors, maternal report of temperament, salivary cortisol, and baseline startle responses at age 4 in a sample of children, some of whom displayed a high frequency of motor activity and negative affect at 4 months of age. Infants who displayed this temperamental profile were reported by their mothers as more shy at age 4 compared with other children. We also found that 4-year-olds who displayed a high frequency of wary behavior during peer play exhibited relatively high morning salivary cortisol, were reported as contemporaneously shy by their mothers, and were behaviorally inhibited at 14 months of age. There were no significant relations found between baseline startle and morning salivary cortisol and measures of shyness at age 4. We speculate that high levels of cortisol in shy children may induce changes in the amygdala, exacerbating their fearfulness.

Behavioral and neuroendocrine responses in shy children

Previous research has shown that infants who display a high frequency of motor activity and negative affect at 4 months of age are likely to be behaviorally inhibited toddlers. We examined social behaviors, maternal report of temperament, salivary cortisol, and baseline startle responses at age 4 in a sample of children, some of whom displayed a high frequency of motor activity and negative affect at 4 months of age. Infants who displayed this temperamental profile were reported by their mothers as more shy at age 4 compared with other children. We also found that 4-year-olds who displayed a high frequency of wary behavior during peer play exhibited relatively high morning salivary cortisol, were reported as contemporaneously shy by their mothers, and were behaviorally inhibited at 14 months of age. There were no significant relations found between baseline startle and morning salivary cortisol and measures of shyness at age 4. We speculate that high levels of cortisol in shy children may induce changes in the amygdala, exacerbating their fearfulness.

Crawling experience is related to changes in cortical organization during infancy: evidence from EEG coherence

Greenough's model of experience-expectant plasticity was used to examine EEG coherence among four groups of 8-month-old infants that varied in hands-and-knees crawling experience. Groups included prelocomotor infants, novice crawlers with 1-4 weeks experience, infants with 5-8 weeks, and long-term crawlers with 9+ weeks experience. Resting EEG was recorded from frontal, parietal, and occipital sites of both hemispheres. EEG coherence between intrahemispheric sites was computed. Novice crawlers (1-4 weeks) displayed greater coherence than either prelocomotor infants or experienced crawlers. These data suggest that the anticipation and onset of locomotion was related to an overproduction of cortico-cortical connections. Pruning of these overabundant connections may be a source of the decrease in coherence as crawling becomes more routine.

Distal movement without headgear: the use of an upper removable appliance for the retraction of upper first molars

The potential hazards and patient resistance to wearing extra-oral appliances are well documented. A method of distalizing molars without the need for head-gear is described.

Individual differences in emotion regulation and behavior problems in preschool children

Emotion regulation (ER) was assessed during a negative mood induction in 79 preschoolers who varied in degree of behavior problems. Facial expressivity during the induction was used to identify 3 ER groups: inexpressive, modulated expressive, and highly expressive. Group differences in ER were significantly related to heart rate and skin conductance. Inexpressive preschoolers had the highest heart rate, lowest vagal tone, and smallest autonomic nervous system (ANS) change during the induction. Highly expressive preschoolers had the slowest heart rate, highest vagal tone, and largest ANS change. The inexpressive and highly expressive groups had more externalizing symptoms than the modulated group at preschool age and at follow-up at the end of 1st grade. Inexpressive preschoolers appeared to have more depressed and anxious symptoms at follow-up.

Perceptions of the risks and benefits of orthodontic treatment

Recent National Health Service changes have brought about a greater involvement of the consumers of medical and dental care in decision making regarding their treatment. The aim of this study was to investigate the level of awareness of the risks and benefits of orthodontic treatment among potential consumers and their referring dentists. Parents of patients referred for orthodontic treatment were issued with a questionnaire about the risks and benefits of treatment and the reason the child had been referred. Study models were also made of the child's teeth. The patients' dentists were issued with a similar questionnaire. The results revealed that most of the parents were aware of the benefits of treatment in general and the reason that their own child required it. This awareness was greater where the orthodontic need on aesthetic grounds was greater. There was less awareness of the risks of treatment though again this was greater among those with a greater need for treatment. When the perceptions of the dentists were evaluated, they were more aware of the risks but were not communicating this to the parents. Since for some patients the risks of treatment may outweigh the benefits, it would be helpful if dentists could provide this information for patients before referral.