First-order phase transitions in solids are notoriously challenging to study. The combination of change in unit cell shape, long range of elastic distortion and flow of latent heat leads to large energy barriers resulting in domain structure, hysteresis and cracking. The situation is worse near a triple point, where more than two phases are involved. The well-known metal-insulator transition in vanadium dioxide, a popular candidate for ultrafast optical and electrical switching applications, is a case in point. Even though VO2 is one of the simplest strongly correlated materials, experimental difficulties posed by the first-order nature of the metal-insulator transition as well as the involvement of at least two competing insulating phases have led to persistent controversy about its nature. Here we show that studying single-crystal VO2 nanobeams in a purpose-built nanomechanical strain apparatus allows investigation of this prototypical phase transition with unprecedented control and precision. Our results include the striking finding that the triple point of the metallic phase and two insulating phases is at the transition temperature, Ttr = Tc, which we determine to be 65.0 ± 0.1 °C. The findings have profound implications for the mechanism of the metal-insulator transition in VO2, but they also demonstrate the importance of this approach for mastering phase transitions in many other strongly correlated materials, such as manganites and iron-based superconductors.

Youth homelessness is a growing concern in the United States. Despite difficulties studying this population due to inconsistent definitions of what it means to be a youth and homeless, the current body of research indicates that abuse, family breakdown, and disruptive family relationships are common contributing factors to youth homelessness. Moreover, the experience of homelessness appears to have numerous adverse implications and to affect neurocognitive development and academics, as well as mental and physical health. Substance use, sexually transmitted infections, and psychiatric disorders are particularly prevalent in this population. Whereas some of these problems may be short-lived, the chronic stress and deprivation associated with homelessness may have long-term effects on development and functioning. Further, difficulties accessing adequate and developmentally-appropriate health care contribute to more serious health concerns. Suggestions for future research and interventions are discussed.

IntroductionAdolescents are a unique and sometimes neglected group in the planning of healthcare services. This is the case in many parts of sub-Saharan Africa, where more than eight out of ten of the world's HIV-infected adolescents live. Although the last decade has seen a reduction in AIDS-related mortality worldwide, largely due to improved access to effective antiretroviral therapy (ART), AIDS remains a significant contributor to adolescent mortality in sub-Saharan Africa. Although inadequate access to ART in parts of the subcontinent may be implicated, research among youth with HIV elsewhere in the world suggests that suboptimal adherence to ART may play a significant role. In this article, we summarize the epidemiology of HIV among sub-Saharan African adolescents and review their adherence to ART, emphasizing the unique challenges and factors associated with adherence behaviour.MethodsWe conducted a comprehensive search of online databases for articles, relevant abstracts, and conference reports from meetings held between 2010 and 2014. Our search terms included “adherence,” “compliance,” “antiretroviral use” and “antiretroviral adherence,” in combination with “adolescents,” “youth,” “HIV,” “Africa,” “interventions” and the MeSH term “Africa South of the Sahara.” Of 19,537 articles and abstracts identified, 215 met inclusion criteria, and 148 were reviewed.DiscussionAdolescents comprise a substantial portion of the population in many sub-Saharan African countries. They are at particular risk of HIV and may experience worse outcomes. Although demonstrated to have unique challenges, there is a dearth of comprehensive health services for adolescents, especially for those with HIV in sub-Saharan Africa. ART adherence is poorer among older adolescents than other age groups, and psychosocial, socio-economic, individual, and treatment-related factors influence adherence behaviour among adolescents in this region. With the exception of a few examples based on affective, cognitive, and behavioural strategies, most adherence interventions have been targeted at adults with HIV.ConclusionsAlthough higher levels of ART adherence have been reported in sub-Saharan Africa than in other well-resourced settings, adolescents in the region may have poorer adherence patterns. There is substantial need for interventions to improve adherence in this unique population.

Rationale: Sleep-disordered breathing (SDB) in children is associated with cognitive challenges. However, potential associations between SDB severity and neurocognitive function, as well as the presence of an SDB cutoff, have not been fully explored.Objectives: To determine whether SDB-associated adverse changes in neurocognitive functioning are severity dependent.Methods: A total of 1,010 snoring and nonsnoring children ages 5-7 years were prospectively recruited from public schools and underwent polysomnography and neurocognitive assessments of intellectual, attention, memory, language, and executive function development. The children were subdivided into four severity groups on the basis of apnea-hypopnea index (AHI), followed by comparisons of cognitive function, with a particular focus on standardized subtests of intellectual, language, attention, memory, and executive function.Measurement and Main Results: Differential Ability Scales Verbal (P , 0.001) and Nonverbal (P = 0.002) performance, as well as global conceptual ability (IQ) (P , 0.001) scores, differed significantly across the groups, with individuals with higher AHI showing worse performance. Additionally, specific NEPSY (a Developmental Neuropsychological Assessment) subscores focused on attention and executive skills differed across the groups, indicating differences in levels of engagement and problem solving. Children with higher AHI (.5 per hour of total sleep time) were significantly more impaired than all three lower AHI groups, indicating a dose-response impact of SDB.Conclusions: This large community-based sample of children highlights the significant deleterious impact of SDB, particularly in children with moderate to severe obstructive sleep apnea, and also that even snoring alone affects neurocognitive function. By affecting developing capabilities, as illustrated by cognitive measures in a severity-graded manner, SDB could adversely impact children's capacity to attain academic and adaptive goals, ultimately hampering their ability to reach independence. Our findings support the need for increased awareness of SDB, with particular emphasis on children with more severe obstructive sleep apnea.

SUMMARYPurpose: Evaluate potential neurocognitive effects of adjunctive levetiracetam in children with inadequately controlled partial-onset seizures (POS). Methods: Randomized, double-blind, placebocontrolled, noninferiority safety study. Children (4-16 years; IQ ‡65) with ‡1 POS during 4 weeks before screening despite taking 1-2 antiepileptic drugs (AEDs) were randomized Levetiracetam was noninferior to placebo because the 90% % CI lower bound was greater than the defined noninferiority margin ()9.0). There were no statistically significant differences between groups in Wide Range Assessment of Memory and Learning-2 indexes and Leiter-R Examiner's Rating Scale scores. Median reductions from baseline in weekly POS frequency were 91.5% % versus 26.5% % for levetiracetam versus placebo; ‡50% % responder rates: 62.5% % versus 41.2% %; seizure freedom rates: 46.9% % versus 8.8% % (ITT). Adverse events were reported by 89.1% % levetiracetam-treated and 85.3% % placebo-treated patients; those reported by ‡10% % levetiracetam patients and more often with levetiracetam were headache, nasopharyngitis, fatigue, vomiting, somnolence, and aggression. Discussion: Neurocognitive effects were no different in pediatric patients with POS treated with adjunctive levetiracetam or placebo. Levetiracetam was effective and well tolerated.