42 research outputs found
Mapping of Axial Strain in InAs/InSb Heterostructured Nanowires
The article presents a mapping of the residual strain along the axis of
InAs/InSb heterostructured nanowires. Using confocal Raman measurements, we
observe a gradual shift in the TO phonon mode along the axis of these
nanowires. We attribute the observed TO phonon shift to a residual strain
arising from the InAs/InSb lattice mismatch. We find that the strain is maximum
at the interface and then monotonically relaxes towards the tip of the
nanowires. We also analyze the crystal structure of the InSb segment through
selected area electron diffraction measurements and electron diffraction
tomography on individual nanowires.Comment: 14 pages, 5 figure
Electronic Band Structure of Wurtzite GaP Nanowires via Resonance Raman Spectroscopy
Raman measurements are performed on defect-free wurzite GaP nanowires.
Resonance Raman measurements are carried out over the excitation energy range
between 2.19 and 2.71 eV. Resonances at 2.38 eV and 2.67 eV of the E1(LO) mode
and at 2.67 eV of the A1(LO) are observed. The presence of these intensity
resonances clearly demonstrates the existence of energy states with Gamma_9hh
and Gamma_7V (Gamma_7C) symmetries of the valence (conduction) band and allows
to measure WZ phase GaP band energies at the Gamma point. In addition, we have
investigated temperature dependent resonant Raman measurements, which allowed
us to extrapolate the zero temperature values of Gamma point energies, along
with the crystal field and spin-orbit splitting energies. Above results provide
a feedback for refining available theoretical calculations to derive the
correct wurtzite III-V semiconductor band structure.Comment: 24 pages, 6 figure
Strain induced band alignment in wurtzite-zincblende InAs heterostructured nanowires
We study band alignment in wurtzite-zincblende polytype InAs heterostructured
nanowires using temperature dependent resonance Raman measurements. Nanowires
having two different wurtzite fractions are investigated. Using visible
excitation wavelengths in resonance Raman measurements, we probe the electronic
band alignment of these semiconductor nanowires near a high symmetry point of
the Brillouin zone (E gap). The strain in the crystal structure, as
revealed from the shift of the phonon mode, explains the observed band
alignment at the wurtzite-zincblende interface. Our experimental results are
further supported by electronic structure calculations for such periodic
heterostructured interface.Comment: 18 pages, 10 figure
Raman sensitivity to crystal structure in InAs nanowires
We report a combined electron transmission and Raman spectroscopy study of
InAs nanowires. We demonstrate that the temperature dependent behavior of
optical phonon energies can be used to determine the relative wurtzite fraction
in the InAs nanowires. Furthermore, we propose that the interfacial strain
between zincblende and wurtzite phases along the length of the wires manifests
in the temperature-evolution of the phonon linewidths. From these studies,
temperature-dependent Raman measurements emerge has a non-invasive method to
study polytypism in such nanowires
Graphene morphology effect on the gas barrier, mechanical and thermal properties of thermoplastic polyurethane
Abstract In this study, we investigated the effect of the morphology of few-layer (FLG) and multi-layer (MLG) graphene flakes on the gas barrier properties of thermoplastic polyurethane (TPU) films. Composite films of TPU filled with FLG and MLG at different concentrations are prepared by solution blending-casting and hot-pressing, achieving an in-plane alignment of the fillers and, consequently, improving the gas barrier properties. Specifically, the hot-pressed TPU composites loaded with 4 wt% of the MLG with a lateral size distribution of 0.1–25.0 μm demonstrates a reduction of ~81% in the gas permeability compared to the pristine TPU. Additionally, the thermal conductivity of the TPU composite (loaded with 4 wt% of MLG) is enhanced ~3 times and the Young modulus increases more than 5 times compared to the pristine TPU
Internal field induced enhancement and effect of resonance in Raman scattering of InAs nanowires
An internal field induced resonant intensity enhancement of Raman scattering
of phonon excitations in InAs nanowires is reported. The experimental
observation is in good agreement with the simulated results for the scattering
of light under varying incident wavelengths, originating from the enhanced
internal electric field in an infinite dielectric cylinder. Our analysis
demonstrates the combined effect of the first higher lying direct band gap
energy (E1) and the refractive index of the InAs nanowires in the internal
field induced resonant Raman scattering. Furthermore, the difference in the
relative contribution of electro-optic effect and deformation potential in
Raman scattering of nanowires and bulk InAs over a range of excitation energies
is discussed by comparing the intensity ratio of their LO and TO phonon modes.Comment: 10 pages, 7 figure
Spatial, temporal, and demographic patterns in prevalence of chewing tobacco use in 204 countries and territories, 1990-2019 : a systematic analysis from the Global Burden of Disease Study 2019
Interpretation Chewing tobacco remains a substantial public health problem in several regions of the world, and predominantly in south Asia. We found little change in the prevalence of chewing tobacco use between 1990 and 2019, and that control efforts have had much larger effects on the prevalence of smoking tobacco use than on chewing tobacco use in some countries. Mitigating the health effects of chewing tobacco requires stronger regulations and policies that specifically target use of chewing tobacco, especially in countries with high prevalence. Findings In 2019, 273 center dot 9 million (95% uncertainty interval 258 center dot 5 to 290 center dot 9) people aged 15 years and older used chewing tobacco, and the global age-standardised prevalence of chewing tobacco use was 4 center dot 72% (4 center dot 46 to 5 center dot 01). 228 center dot 2 million (213 center dot 6 to 244 center dot 7; 83 center dot 29% [82 center dot 15 to 84 center dot 42]) chewing tobacco users lived in the south Asia region. Prevalence among young people aged 15-19 years was over 10% in seven locations in 2019. Although global agestandardised prevalence of smoking tobacco use decreased significantly between 1990 and 2019 (annualised rate of change: -1 center dot 21% [-1 center dot 26 to -1 center dot 16]), similar progress was not observed for chewing tobacco (0 center dot 46% [0 center dot 13 to 0 center dot 79]). Among the 12 highest prevalence countries (Bangladesh, Bhutan, Cambodia, India, Madagascar, Marshall Islands, Myanmar, Nepal, Pakistan, Palau, Sri Lanka, and Yemen), only Yemen had a significant decrease in the prevalence of chewing tobacco use, which was among males between 1990 and 2019 (-0 center dot 94% [-1 center dot 72 to -0 center dot 14]), compared with nine of 12 countries that had significant decreases in the prevalence of smoking tobacco. Among females, none of these 12 countries had significant decreases in prevalence of chewing tobacco use, whereas seven of 12 countries had a significant decrease in the prevalence of tobacco smoking use for the period. Summary Background Chewing tobacco and other types of smokeless tobacco use have had less attention from the global health community than smoked tobacco use. However, the practice is popular in many parts of the world and has been linked to several adverse health outcomes. Understanding trends in prevalence with age, over time, and by location and sex is important for policy setting and in relation to monitoring and assessing commitment to the WHO Framework Convention on Tobacco Control. Methods We estimated prevalence of chewing tobacco use as part of the Global Burden of Diseases, Injuries, and Risk Factors Study 2019 using a modelling strategy that used information on multiple types of smokeless tobacco products. We generated a time series of prevalence of chewing tobacco use among individuals aged 15 years and older from 1990 to 2019 in 204 countries and territories, including age-sex specific estimates. We also compared these trends to those of smoked tobacco over the same time period. Findings In 2019, 273 & middot;9 million (95% uncertainty interval 258 & middot;5 to 290 & middot;9) people aged 15 years and older used chewing tobacco, and the global age-standardised prevalence of chewing tobacco use was 4 & middot;72% (4 & middot;46 to 5 & middot;01). 228 & middot;2 million (213 & middot;6 to 244 & middot;7; 83 & middot;29% [82 & middot;15 to 84 & middot;42]) chewing tobacco users lived in the south Asia region. Prevalence among young people aged 15-19 years was over 10% in seven locations in 2019. Although global age standardised prevalence of smoking tobacco use decreased significantly between 1990 and 2019 (annualised rate of change: -1 & middot;21% [-1 & middot;26 to -1 & middot;16]), similar progress was not observed for chewing tobacco (0 & middot;46% [0 & middot;13 to 0 & middot;79]). Among the 12 highest prevalence countries (Bangladesh, Bhutan, Cambodia, India, Madagascar, Marshall Islands, Myanmar, Nepal, Pakistan, Palau, Sri Lanka, and Yemen), only Yemen had a significant decrease in the prevalence of chewing tobacco use, which was among males between 1990 and 2019 (-0 & middot;94% [-1 & middot;72 to -0 & middot;14]), compared with nine of 12 countries that had significant decreases in the prevalence of smoking tobacco. Among females, none of these 12 countries had significant decreases in prevalence of chewing tobacco use, whereas seven of 12 countries had a significant decrease in the prevalence of tobacco smoking use for the period. Interpretation Chewing tobacco remains a substantial public health problem in several regions of the world, and predominantly in south Asia. We found little change in the prevalence of chewing tobacco use between 1990 and 2019, and that control efforts have had much larger effects on the prevalence of smoking tobacco use than on chewing tobacco use in some countries. Mitigating the health effects of chewing tobacco requires stronger regulations and policies that specifically target use of chewing tobacco, especially in countries with high prevalence. Copyright (c) 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.Peer reviewe
Global injury morbidity and mortality from 1990 to 2017 : results from the Global Burden of Disease Study 2017
Correction:Background Past research in population health trends has shown that injuries form a substantial burden of population health loss. Regular updates to injury burden assessments are critical. We report Global Burden of Disease (GBD) 2017 Study estimates on morbidity and mortality for all injuries. Methods We reviewed results for injuries from the GBD 2017 study. GBD 2017 measured injury-specific mortality and years of life lost (YLLs) using the Cause of Death Ensemble model. To measure non-fatal injuries, GBD 2017 modelled injury-specific incidence and converted this to prevalence and years lived with disability (YLDs). YLLs and YLDs were summed to calculate disability-adjusted life years (DALYs). Findings In 1990, there were 4 260 493 (4 085 700 to 4 396 138) injury deaths, which increased to 4 484 722 (4 332 010 to 4 585 554) deaths in 2017, while age-standardised mortality decreased from 1079 (1073 to 1086) to 738 (730 to 745) per 100 000. In 1990, there were 354 064 302 (95% uncertainty interval: 338 174 876 to 371 610 802) new cases of injury globally, which increased to 520 710 288 (493 430 247 to 547 988 635) new cases in 2017. During this time, age-standardised incidence decreased non-significantly from 6824 (6534 to 7147) to 6763 (6412 to 7118) per 100 000. Between 1990 and 2017, age-standardised DALYs decreased from 4947 (4655 to 5233) per 100 000 to 3267 (3058 to 3505). Interpretation Injuries are an important cause of health loss globally, though mortality has declined between 1990 and 2017. Future research in injury burden should focus on prevention in high-burden populations, improving data collection and ensuring access to medical care.Peer reviewe