SnP₃: A Previously Unexplored Two-Dimensional Material

We predict SnP₃ to be an easily exfoliable and dynamically stable two-dimensional (2D) material with thickness-dependent electronic properties. On the basis of density functional theory calculations, we show that mono- and bilayer SnP₃ has relatively low cleavage energies of 0.71 and 0.45 J m^–2, lower than several other 2D materials and comparable to that of graphene (0.32 J m^–2). Mono- and bilayer SnP₃ have an indirect band gap of 0.83 and 0.55 eV, respectively, and the magnitude of the gap can be tuned by applying strain. Remarkably, pristine monolayer SnP₃ has a relatively high carrier mobility in the range of 3000–7000 cm² V^–1 s^–1, at par with well-known 2D semiconductors such as MoS₂, phosphorene, and other phosphorus-based layered materials such as GeP₃ and InP₃. Mono- and bilayer SnP₃ also show large optical absorption, resulting from the existence of the van-Hove singularities in the electronic density of states. The combined properties of layered SnP₃, in particular, its high carrier mobility and tunable band gap, along with large optical absorption coefficient, open up interesting possibilities for nanoelectronic and nanophotonic applications

Thickness and Stacking Dependent Polarizability and Dielectric Constant of Graphene–Hexagonal Boron Nitride Composite Stacks

The giant carrier mobility of graphene is significantly reduced due to external perturbations, such as substrate based charge impurities, and their impact can be minimized by encapsulating graphene between hexagonal boron nitride (hBN) layers. Using density functional theory (DFT) based ab initio calculations, we study the static response of such a composite by placing it in a vertical electric field. We find that at relatively low electric field (∼0.1 V/Å), although the relative permittivity (ε_r) of a composite stack increases with the number of layers, ε_r for a fixed stack thickness is independent of the field strength. However, at higher electric field strength, ε_r increases monotonically with the applied field strength even for a fixed stack thickness, signifying nonlinear response. The relative permittivity changes more readily for graphene rich stacks as compared to hBN rich stacks, which is consistent with the property of the pristine phases. We also present an empirical formulation to calculate the thickness and stacking dependent effective dielectric constant of any arbitrary stack of graphene–hBN layers, which fits very well with the ab initio calculations. Our empirical formulation will also be applicable for van der Waals stacks of other two-dimensional materials and will be useful for designing and interpreting transport experiments, where electrostatic effects such as capacitance and charge screening are important

Characteristics of included studies.

<p>Characteristics of included studies.</p

Forest plot showing the proportion of IPD from hospital-based prospective studies in South Asian children less than 5 years of age with confirmed invasive bacterial disease.

<p>The plot also shows a subgroup analysis for the pneumococcal pneumonia cases among all the bacterial pneumonia patients and for the pneumococcal meningitis cases among all of the pyogenic meningitis patients.</p

Forest plot showing the proportion of IPD from hospital-based prospective studies in South Asian children under the age of 5 with suspected invasive bacterial disease.

<p>The plot also shows a subgroup analysis for the pneumococcal pneumonia cases among all of the pneumonia patients and for the pneumococcal meningitis cases among all of the meningitis patients.</p

Corrected funnel plot using the trim and fill method.

<p>Corrected funnel plot using the trim and fill method.</p

Distribution of Serotypes, Vaccine Coverage, and Antimicrobial Susceptibility Pattern of Streptococcus Pneumoniae in Children Living in SAARC Countries: A Systematic Review

<div><p>Introduction</p><p>Each SAARC nation falls in the zone of high incidence of pneumococcal disease but there is a paucity of literature estimating the burden of pneumococcal disease in this region.</p><p>Objective</p><p>To identify the prevalent serotypes causing invasive pneumococcal disease in children of SAARC countries, to determine the coverage of these serotypes by the available vaccines, and to determine the antibiotic resistance pattern of <i>Streptococcus pneumoniae</i>.</p><p>Methods</p><p>We searched major electronic databases using a comprehensive search strategy, and additionally searched the bibliography of the included studies and retrieved articles till July 2014. Both community and hospital based observational studies which included children aged ≤12 years as/or part of the studied population in SAARC countries were included.</p><p>Results</p><p>A total of 17 studies were included in the final analysis. The period of surveillance varied from 12–96 months (median, 24 months). The most common serotypes country-wise were as follows: serotype 1 in Nepal; serotype 14 in Bangladesh and India; serotype 19F in Sri Lanka and Pakistan. PCV-10 was found to be suitable for countries like India, Nepal, Bangladesh, and Sri Lanka, whereas PCV-13 may be more suitable for Pakistan. An increasing trend of non-susceptibility to antibiotics was noted for co-trimoxazole, erythromycin and chloramphenicol, whereas an increasing trend of susceptibility was noted for penicillin.</p><p>Conclusion</p><p>Due to paucity of recent data in majority of the SAARC countries, urgent large size prospective studies are needed to formulate recommendations for specific pneumococcal vaccine introduction and usage of antimicrobial agents in these regions.</p></div

Burden of Invasive Pneumococcal Disease in Children Aged 1 Month to 12 Years Living in South Asia: A Systematic Review

<div><p>Objective</p><p>The primary objective was to estimate the burden of invasive pneumococcal disease (IPD) in children aged 1 month to 12 years in South Asian countries.</p><p>Methods</p><p>We searched three electronic databases (PubMed, Embase and the Cochrane Library) using a comprehensive search strategy, we manually searched published databases (Index Medicus and Current Contents) and we also searched the bibliographies of the included studies and retrieved reviews. The searches were current through June 2013. Eligible studies (community-based and hospital-based) were pooled and a separate analysis for India was also completed. A meta-regression analysis and heterogeneity analysis were performed. The protocol was registered with PROSPERO registration number CRD42013004483.</p><p>Results</p><p>A total of 22 studies surveying 36,714 children were included in the systematic review. Hospital-based prospective studies from South Asia showed that 3.57% of children had IPD, and 15% of all bacterial pneumonia cases were due to <i>Streptococcus pneumoniae</i>. Indian studies showed that the incidence of IPD was 10.58% in children admitted to hospitals with suspected invasive bacterial diseases, and 24% of all bacterial pneumonia cases were due to <i>S. pneumonia</i>. Population-based studies from South Asian countries showed that 12.8% of confirmed invasive bacterial diseases were caused by <i>S. pneumonia</i> whereas retrospective hospital-based studies showed that 28% of invasive bacterial diseases were due to <i>S. pneumoniae</i>. Meta-regression showed that there was a significant influence of the antigen testing method for diagnosing IPD on IPD prevalence.</p><p>Conclusion</p><p><i>S. pneumoniae</i> is responsible for a substantial bacterial disease burden in children of South Asian countries including India despite the presence of high heterogeneity in this meta-analysis. Treatment guidelines must be formulated, and preventive measures like vaccines must also be considered.</p></div

Funnel plot showing the publication bias.

<p>Funnel plot showing the publication bias.</p

Characteristics of excluded studies.

<p>Characteristics of excluded studies.</p