Buffer breakdown in GaN-on-Si HEMTs: A comprehensive study based on a sequential growth experiment

Abstract The aim of this work is to investigate the breakdown mechanisms of the layers constituting the vertical buffer of GaN-on-Si HEMTs; in addition, for the first time we demonstrate that the breakdown field of the AlN nucleation layer grown on a silicon substrate is equal to 3.2 MV/cm and evaluate its temperature dependence. To this aim, three samples, obtained by stopping the epitaxial growth of a GaN on Silicon stack at different steps, are studied and compared: Si/AlN, Si/AlN/AlGaN, full vertical stack up to the Carbon doped buffer layer. The current-voltage (IV) characterizations performed at both room temperature and high temperature show that: (i) the defectiveness of the AlN nucleation layer is the root cause of the leakage through an AlN/Silicon junction, and causes the vertical I-V characteristics to have a high device-to-device variability; (ii) the first AlGaN layer grown over the AlN, beside improving the breakdown voltage of the whole structure, causes the leakage current to be more stable and uniform across the sample area; (iii) a thick strain-relief stack and a carbon-doped GaN buffer enhance the breakdown voltage up to more than 750 V at 170 °C, and guarantee a remarkably low device-to-device variability. Furthermore, a set of constant voltage stress on the Si/AlN sample demonstrate that the aluminum nitride layer shows a time dependent breakdown, with Weibull-distributed failures and a shape factor greater than 1, in line with the percolation model

Mental health issues in unaccompanied refugee minors

Previous studies about unaccompanied refugee minors (URMs) showed that they are a highly vulnerable group who have greater psychiatric morbidity than the general population. This review focuses on mental health issues among URMs. Articles in databases PsycINFO, Medline and PubMed from 1998 to 2008 addressing this topic were reviewed. The literature had a considerable emphasis on the assessment of PTSD symptoms. Results revealed higher levels of PTSD symptoms in comparison to the norm populations and accompanied refugee minors. In several studies, age and female gender predicted or influenced PTSD symptoms. The existing literature only permits limited conclusions on this very hard to reach population. Future research should include the analysis of long-term outcomes, stress management and a more thorough analysis of the whole range of psychopathology. Additionally, the development of culturally sensitive norms and standardized measures for diverse ethnic groups is of great importance

Recommendation of RILEM TC 271-ASC: New accelerated test procedure for the assessment of resistance of natural stone and fired-clay brick units against salt crystallization

This recommendation is devoted to testing the resistance of natural stone and fired-clay brick units against salt crystallization. The procedure was developed by the RILEM TC 271-ASC to evaluate the durability of porous building materials against salt crystallization through a laboratory method that allows for accelerated testing without compromising the reliability of the results. The new procedure is designed to replicate salt damage caused by crystallization near the surface of materials as a result of capillary transport and evaporation. A new approach is proposed that considers the presence of two stages in the salt crystallization test. In the first, the accumulation stage, salts gradually accumulate on or near the surface of the material due to evaporation. In the second, the propagation stage, damage initiates and develops due to changes in moisture content and relative humidity that trigger salt dissolution and crystallization cycles. To achieve this, two types of salt were tested, namely sodium chloride and sodium sulphate, with each salt tested separately. A methodology for assessing the salt-induced damage is proposed, which includes visual and photographical observations and measurement of material loss. The procedure has been preliminarily validated in round robin tests

Examining the psychological wellbeing of refugee children and the role of friendship and bullying

BACKGROUND: Refugee children might have experienced violent and traumatic events before settling into a new country. In the United Kingdom, the number of refugee children is increasing; however, little is known about their psycho-social and physical well-being. AIM: This study aims to investigate the psychological well-being and behaviour of refugee children compared to British-born children on a number of psychological, social, behavioural, and health-related issues and to investigate the role of friendship as a protective factor. SAMPLES: This study utilized a sample of 149 refugee children recruited from two charities, 79 of which are children aged 6-10 years and 70 older refugee children aged 11-16 years. The study also included 120 non-refugee children recruited from primary schools aged 6-10 years. METHODS: This is a cross-sectional study that investigates the psycho-social well-being of refugee children compared to non-refugee British-born children. The study explored symptoms of posttraumatic stress disorder, emotional and behavioural problems (Strengths and Difficulties Questionnaire), self-esteem, friendships and popularity, bullying and victimization, physical health, and psychosomatic problems. RESULTS: Young refugee children reported more peer problems, functional impairment, physical health, and psychosomatic problems compared to the control children and older refugee children groups. On the other hand, older refugee children had lower self-esteem (academic and social self-peers) compared to the younger refugee children group. The differences between the groups were explained by friendship quality, number of friends, peer bullying/victimization, or sibling bullying/victimization except for physical health and psychosomatic problems. CONCLUSIONS: While refugee children were found to be at risk on various levels, the findings also point to the fact that social relationships including friendship quality and number of friends played an essential protective role. Conversely, bullying was a risk factor that explained many of the refugees' problems. These findings pave the way for future research to further probe into the well-being of refugee children in the United Kingdom while also targeting relevant intervention schemes specifically tailored to address their needs

shaping the deserving refugee insights from a local reception programme in belgium

The sudden increase of asylum applications in the aftermath of the 2015 "refugee crisis", has sparked the debate on the concept of "deservingness" in public discourse. Who deserves to enter into European territory? Who deserves to receive state-funded assistance? This article unpacks the notion of "deservingness" by analysing the rationalities of care underpinning a European-funded local support programme in Antwerp (Belgium). The programme offers special assistance to former unaccompanied minors, recognised as beneficiaries of legal protection, who have recently turned 18. By examining the categories, attitudes and perceptions shaping this local project, we show how the idea of "deservingness", a central notion in wider European discourses on refugee reception, is reproduced and critically implemented by local actors of refugee assistance. Drawing on focus group interviews with five municipal and civil society organizations, we untangle legal, moral and economic dimensions of deservingness and illustrate how these can overlap or contradict each other within stakeholders' perspectives. The analysis of the different stakeholders' perspectives about the assumed characteristics of this "new" category of refugees deserving special care shows the significance of stakeholders' respective organisational backgrounds. On a deeper level, ideas on deservingness reflect stakeholders' different aspirations about the kind of citizens young refugees should become. As such, this chapter contributes to deeper understanding of moralities and rationalities shaping public discourse and local reception of refugees in Europe. It also highlights the role of localities in shaping innovative policies and in the wider debate on refugee assistance

Reintegration of child soldiers in Burundi: A tracer study

Background Substantial attention and resources are aimed at the reintegration of child soldiers, yet rigorous evaluations are rare. Methods This tracer study was conducted among former child soldiers (N=452) and never-recruited peers (N=191) who participated in an economic support program in Burundi. Socio-economic outcome indicators were measured retrospectively for the period before receiving support (T1; 2005–06); immediately afterwards (T2; 2006–07); and at present (T3; 2010). Participants also rated present functional impairment and mental health indicators. Results Participants reported improvement on all indicators, especially economic opportunity and social integration. At present no difference existed between both groups on any of the outcome indicators. Socio-economic functioning was negatively related with depression- and, health complaints and positively with intervention satisfaction. Conclusion The present study demonstrates promising reintegration trajectories of former child soldiers after participating in a support program

PTSD, depression and anxiety among former abductees in Northern Uganda

<p>Abstract</p> <p>Background</p> <p>The population in Northern Uganda has been exposed to extreme levels of traumatic stress and thousands abducted forcibly became rebel combatants.</p> <p>Methods</p> <p>Using structured interviews, the prevalence and severity of posttraumatic stress disorder (PTSD), depression and anxiety was assessed in 72 former abducted adults, 62 of them being former child soldiers.</p> <p>Results</p> <p>As retrospective reports of exposure to traumatic stress increased, anxiety and PTSD occurrence increased (r = .45). 49% of respondents were diagnosed with PTSD, 70% presented with symptoms of depression, and 59% with those of anxiety. In a multiple linear regression analysis four factors could best explain the development of PTSD symptoms: male respondents (sex) living in an IDP-Camp (location) with a kinship murdered in the war (family members killed in the war) and having experienced a high number of traumatic events (number of traumatic events) were more likely to develop symptoms of PTSD than others. In disagreement to a simple dose-response-effect though, we also observed a negative correlation between the time spent with the rebels and the PTSD symptom level.</p> <p>Conclusions</p> <p>Former abductees continue to suffer from severe mental ill-health. Adaptation to the living condition of rebels, however, may lower trauma-related mental suffering.</p

Screening for Posttraumatic Stress Disorder among Somali ex-combatants: A validation study

In Somalia, a large number of active and former combatants are affected by psychological problems such as Posttraumatic Stress Disorder (PTSD), that impairs their ability to re-integrate into civilian life. This study reports on development and validation of a screening tool for PTSD in Somali language with a sample of ex-combatants.Waxaa Soomaaliya ka jira tiro badan oo askartii hore ah oo dhimirka wax ka gaaray, sida cudurka la yiraahdo "Posttraumatic Stress Disorder (PTSD)", kaaso isbeddel ku sameeyo qofka dad ladhaqankiisa. Darasaadkanina wuxuu horumarinayaa qalabka baaritaanka caafimaadka cudurka DPTS oo loo adeegsanayo Af-soomaaliga.In Somalia, un gran numero di soldati o ex-soldati sono affetti da problemi psicologici come il Disturbo Post-Traumatico da Stress (DPTS), che altera la capacità di re-integrarsi nella vita civile. Questo studio riporta sullo sviluppo di uno strumento di screening per il DPTS in lingua somala