Mesoscopic phase separation in Nax_xCoO2_2 (0.65≤x≤0.750.65\leq x\leq 0.75)

NMR, EPR and magnetization measurements in Na$_x$CoO$_2$ for $0.65\leq x\leq 0.75$ are presented. While the EPR signal arises from Co$^{4+}$ magnetic moments ordering at $T_c\simeq 26$ K, $^{59}$Co NMR signal originates from cobalt nuclei in metallic regions with no long range magnetic order and characterized by a generalized susceptibility typical of strongly correlated metallic systems. This phase separation in metallic and magnetic insulating regions is argued to occur below $T^*(x)$ ($220 - 270$ K). Above $T^*$ an anomalous decrease in the intensity of the EPR signal is observed and associated with the delocalization of the electrons which for $T<T^*$ were localized on Co$^{4+}$ $d_{z^2}$ orbitals. It is pointed out that the in-plane antiferromagnetic coupling $J\ll T^*$ cannot be the driving force for the phase separation.Comment: 14 figure

Health risk behaviours among adolescents in the English-speaking Caribbean: a review

<p>Abstract</p> <p>Background</p> <p>The aim of this paper was to review and summarize research on prevalence of health risk behaviours, their outcomes as well as risk and protective factors among adolescents in the English-speaking Caribbean.</p> <p>Methods</p> <p>Searching of online databases and the World Wide Web as well as hand searching of the <it>West Indian Medical Journal </it>were conducted. Papers on research done on adolescents aged 10 – 19 years old and published during the period 1980 – 2005 were included.</p> <p>Results</p> <p>Ninety-five relevant papers were located. Five papers were published in the 1980s, 47 in the 1990s, and from 2000–2005, 43 papers. Health risk behaviours and outcomes were divided into seven themes. Prevalence data obtained for these, included lifetime prevalence of <b>substance use</b>: cigarettes-24% and marijuana-17%; <b>high risk sexual behaviour</b>: initiation of sexual activity ≤ 10 years old-19% and those having more than six partners-19%; <b>teenage pregnancy</b>: teens account for 15–20% of all pregnancies and one-fifth of these teens were in their second pregnancy; <b>Sexually-Transmitted Infections (STIs)</b>: population prevalence of gonorrhoea and/or chlamydia in 18–21 year-olds was 26%; <b>mental health</b>: severe depression in the adolescent age group was 9%, and attempted suicide-12%; <b>violence and juvenile delinquency</b>: carrying a weapon to school in the last 30 days-10% and almost always wanting to kill or injure someone-5%; <b>eating disorders and obesity</b>: overweight-11%, and obesity-7%. Many of the risk behaviours in adolescents were shown to be related to the adolescent's family of origin, home environment and parent-child relationships. Also, the protective effects of family and school connectedness as well as increased religiosity noted in studies from the United States were also applicable in the Caribbean.</p> <p>Conclusion</p> <p>There is a substantial body of literature on Caribbean adolescents documenting prevalence and correlates of health risk behaviours. Future research should emphasize the designing and testing of interventions to alleviate this burden.</p

Antibiotic exposure in the first two years of life and development of asthma and other allergic diseases by 7.5 yr: A dose‐dependent relationship

To cite this article: Hoskin-Parr L, Teyhan A, Blocker A, Henderson AJW. Antibiotic exposure in the first two years of life and development of asthma and other allergic diseases by 7.5 yr: a dose-dependent relationship. Pediatr Allergy Immunol 2013: 24: 762–771. BACKGROUND: Antibiotic use in infancy disrupts gut microflora during a critical period for immune system development. It is hypothesized that this could predispose to the development of allergic diseases. We investigated the associations of antibiotic use in the first 2 yr of life with the development of asthma, eczema or hay fever by age 7.5 yr in a longitudinal birth cohort. METHODS: Subjects were 4952 children from the Avon Longitudinal Study of Parents and Children (ALSPAC). Child antibiotic use and asthma, eczema and hay fever symptoms were maternally reported. Atopy was assessed by skin prick tests at age 7.5 yr. The total number of antibiotic courses was considered as the main exposure. Data were analysed using multivariate logistic regression. RESULTS: Children reported to have taken antibiotics during infancy (0–2 yr) were more likely to have asthma at 7.5 yr (OR 1.75, 95% CI 1.40–2.17), and the odds (OR, [95% CI]) increased with greater numbers of courses: once 1.11 [0.84–1.48]; twice 1.50 [1.14–1.98]; three times 1.79 [1.34–2.40]; four times or more 2.82 [2.19–3.63]. Increased antibiotic use was also associated with higher odds of eczema and hay fever but not atopy. The effect appeared to be associated with cumulative rather than a critical period of exposure during the first 2 yr. CONCLUSIONS: A robust and dose-dependent association was found between antibiotic use in the first 2 yr of life and asthma at age 7.5 yr but did not appear to be mediated through an association with atopy

NaAlH4 Nanoconfinement in a Mesoporous Carbon for Application in Lithium Ion Batteries

Alanates have recently attracted attention as new anodic materials for lithium ion batteries. The electrochemical activity of sodium alanate has been already reported and the conversion mechanism explained. Through a complex conversion reaction, this compound is able to develop almost all the theoretical capacity, achieving more than 1700 mAh/g upon first discharge with an efficiency of 70%. Nevertheless alanate undergoes to capacity fade in few cycles. This is mainly due to the severe structural reorganization following the conversion reaction, that results in electrode pulverization and loss of electric contact. Here, we present a nanocomposite material consisting of NaAlH4 confined in the nanoporous of a carbon matrix able to mitigate the effect of volume expansion and improve the cyclability. Specifically, the nanocomposite has been studied in terms of structure, morphology and hydrogen content by the means of Infrared Spectroscopy, solid state NMR, electronic microscopy and thermal analysis. Finally, its performance in lithium cells is presented. © 2017 The Electrochemical Society. All rights reserved

Tin-coated graphite electrodes as composite anodes for Li-ion batteries. Effects of tin coatings thickness toward intercalation behavior.

Theelectrochemicalbehaviorofgraphiteanodes,coatedby50–500A ̊-thickSnlayers,isdiscussedin the present paper. Morphology and structure of the modified electrode surfaces are described, and the charge/discharge behavior is evaluated by galvanostatic cycles at temperatures down to −30◦C. The enhanced kinetics of the intercalation/deintercalation process is studied by cyclic voltammetry and electrochemical impedance spectroscopy, focusing on the role played by the Sn coatings in the inter- calation/deintercalation mechanism. The results show that the metal layers modify and stabilize the electrode/electrolyte interphase and that the intercalation process is mediated by reversible Li–Sn alloys formation. Moreover, all the Sn coatings are effective in modifying the energy barriers related both to the Li+ desolvation step and to the migration of the desolvated Li+ ion through the modified surface layers. As a consequence, the overall polarization for the charge-transfer process is reduced, and enhanced low-temperature intercalation performances are obtained

Investigation of the Effects of Mechanochemical Treatment on NaAlH4 Based Anode Materials for Li-Ion Batteries

Sodium alanate has proven to be a feasible candidate for electrochemical applications. Within a lithium cell, NaAlH4 closely approaches its theoretical capacity of 1985 mAhg−1 upon the first discharge. Despite its high specific capacity, NaAlH4 suffers from poor cycle efficiency, mostly due to the severe volume expansion following the conversion reaction and resulting in damage to electrode mechanical integrity with loss of electrical contact. Synthesis of an appropriate composite alanate/carbon by high energy ball milling demonstrates an ability to mitigate these deleterious effects, whereby large improvements in terms of electrochemical reversibility can be achieved. In order to highlight the effects of mechanochemical treatment on the electrochemical properties of NaAlH4, new insights on such NaAlH4/C composites are reported. Solid state NMR has been used to study the impact of ball milling on the NaAlH4 crystal structure, while, the hydrogen content and associated desorption properties have been evaluated by thermal programmed desorption measurements. Also, electrochemical features have been analyzed via the combined application of potentiodynamic cycling with galvanostatic acceleration and electrochemical impedance spectroscopy measurements. Finally, new evidence concerning the reversibility of the conversion processes has been obtained by ex-situ NMR measurements on cycled electrodes

Magnetic resonance studies of chemically intercalated Li xV 2O 5 aerogels

7Li, 51V solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) measurements have been performed upon chemically lithiated Li xV 2O 5 aerogels, with compositions of 1.00&lt;5.84. These compounds can intercalate reversibly large amounts of Li + and, therefore, are of interest as battery cathodes. Still, the mechanism regarding the electron transfer from an inserted lithium metal to a host aerogel V 2O 5 and details regarding the lithium cation environments are not fully understood. Li xV 2O 5 crystals are known to exhibit various structural phase changes and, when multiple phases are present, the capability of the material to intercalate reversibly appears to be adversely affected. On the other hand, aerogels have no such multiphase behavior and aerogel based cathodes exhibit greater stability upon cycling. NMR shows that neither the structure nor the dynamics vary greatly with the amount of lithium content, and that the lithiated aerogel is best described as a single-phase material. Characterization of lithium and vanadium sites is performed through analysis of both NMR and EPR spectra. 7Li line shapes are affected by first-order quadrupolar, magnetic dipolar interactions and motional narrowing. At and above room temperature, relaxation is governed primarily by a quadrupolar mechanism. NMR derived activation energies and diffusion coefficients are different from those of bronzes and electrochemically intercalated V 2O 5. 51V NMR lines, indicative of the presence of V 5+ at all compositions, undergo diamagnetic shifts of up to about 50 ppm with an increase in lithium content. These results imply the presence of oxidized impurities or electronic charge delocalization. Additionally, EPR measurements provide evidence of VO 2+ impurities and indirect evidence of nonbridging oxygen at high lithium contents. © 2002 American Institute of Physics