Association between cord blood 25-hydroxyvitamin D concentrations and respiratory tract infections in the first 6 months of age in a Korean population: a birth cohort study (COCOA)

PurposePrevious studies suggest that the concentration of 25-hydroxyvitamin D [25(OH)D] in cord blood may show an inverse association with respiratory tract infections (RTI) during childhood. The aim of the present study was to examine the influence of 25(OH)D concentrations in cord blood on infant RTI in a Korean birth cohort.MethodsThe levels of 25(OH)D in cord blood obtained from 525 Korean newborns in the prospective COhort for Childhood Origin of Asthma and allergic diseases were examined. The primary outcome variable of interest was the prevalence of RTI at 6-month follow-up, as diagnosed by pediatricians and pediatric allergy and pulmonology specialists. RTI included acute nasopharyngitis, rhinosinusitis, otitis media, croup, tracheobronchitis, bronchiolitis, and pneumonia.ResultsThe median concentration of 25(OH)D in cord blood was 32.0 nmol/L (interquartile range, 21.4 to 53.2). One hundred and eighty neonates (34.3%) showed 25(OH)D concentrations less than 25.0 nmol/L, 292 (55.6%) showed 25(OH)D concentrations of 25.0-74.9 nmol/L, and 53 (10.1%) showed concentrations of ≥75.0 nmol/L. Adjusting for the season of birth, multivitamin intake during pregnancy, and exposure to passive smoking during pregnancy, 25(OH)D concentrations showed an inverse association with the risk of acquiring acute nasopharyngitis by 6 months of age (P for trend=0.0004).ConclusionThe results show that 89.9% of healthy newborns in Korea are born with vitamin D insufficiency or deficiency (55.6% and 34.3%, respectively). Cord blood vitamin D insufficiency or deficiency in healthy neonates is associated with an increased risk of acute nasopharyngitis by 6 months of age. More time spent outdoors and more intensified vitamin D supplementation for pregnant women may be needed to prevent the onset of acute nasopharyngitis in infants

Chemoprevention of Gastric Cancer: Statins

Gastric cancer is one of the leading causes of cancer-related deaths worldwide. Because the gastric cancer-related mortality rate is expected to increase, chemo-preventive strategies for gastric cancer are required. Statins inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase, the enzyme involved in the rate-limiting step in cholesterol synthesis. Several studies have shown that statins have potential protective effects against gastric cancer; however, other studies have reported contradictory results. Therefore, further studies are needed to clarify the role of statins in the chemoprevention of gastric cancer

Ignition characteristics of a temporally evolving n-heptane jet in an iso-octane/air stream under RCCI combustion-relevant conditions

The ignition characteristics of a temporally-evolving n-heptane jet in an iso-octane/air stream under reactivity controlled compression ignition (RCCI) combustion-relevant conditions are investigated using 2-D direct numerical simulations (DNSs) with a 116-species primary reference fuel (PRF)/air reduced mechanism. For the DNSs of RCCI combustion, iso-octane and n-heptane are chosen as two different fuels delivered by the port-fuel and direct-fuel injections, respectively. Therefore, the ignition characteristics of both fuels can be investigated by simulating the ignition of a temporally-evolving n-heptane jet with relative jet velocity, U0, within iso-octane/air charge. It is found that the first-stage ignition kernels governed by the low-temperature chemistry first develop primarily within the n-heptane jet near the mixing layer regardless of U0, and evolve into low-temperature flames, propagating into relatively fuel-rich mixtures in the n-heptane jet. High-temperature flames also develop first in the n-heptane jet, following the trajectories of low-temperature flames, and then, propagate towards both relatively fuel-lean mixtures of the iso-octane/air charge and fuel-rich mixtures of the n-heptane jet. They keep propagating into fuel-lean mixtures and finally end-gas auto-ignition occurs. It is also found that the first-stage ignition occurs more quickly with increasing U0 due to enhanced mixing between relatively cold n-heptane jet and hot iso-octane/air charge, and consequently, the second-stage ignition also advances in time with increasing U0, which are opposite to the results found in previous DNSs of RCCI combustion. Such ignition characteristics are more likely to prolong the overall combustion duration and reduce the peak of heat release rate with increasing U0. In addition, chemical explosive mode analysis (CEMA) identifies important variables and reactions for the low-, intermediate-, and high-temperature chemistries under such RCCI conditions

A DNS Study of the Effects of Shear Velocity on the Ignition of a Lean PRF/air Mixture with n-Heptane Stream under RCCI Conditions

The effects of shear velocity on the ignition characteristics of a lean primary reference fuel (PRF)/air mixture with an n-heptane stream under reactivity controlled compression ignition (RCCI) conditions are investigated using 2-D direct numerical simulations (DNSs) with a 116-species PRF/air reduced mechanism. For RCCI combustion, iso-octane and n-heptane are chosen as two different fuels which have low and high reactivity, respectively. The effects of the n-heptane stream on the ignition of PRF/ air mixture are investigated by varying relative mixing layer velocity, U0, developed between the portinjected iso-octane/air stream and directly-injected n-heptane stream. It is found that the first-stage ignition kernels governed by the low temperature chemistry develop primarily near the mixing layer in the n-heptane stream and evolve into low temperature flames, propagating into relatively fuel-rich mixtures. High temperature flames also develop in the n-heptane stream, following the trajectories of low temperature flames and propagate toward both relatively fuel-lean and fuel-rich mixtures. The high temperature flames keep propagating into fuel-lean mixtures and finally, the end-gas auto-ignition occurs. As such, both the first- and second-stage ignitions are found to be advanced in time with increasing U0, which is opposite to the results in previous DNSs of RCCI combustion with homogeneous turbulence. From the chemical explosive mode analysis (CEMA), important variables and reactions to the low-, intermediate-, and high-temperature chemistries under RCCI condition are identified

Direct numerical simulations of the ignition of temporally evolving n-heptane jet under RCCI combustion-relevant conditions

The ignition characteristics of a temporally evolving n-heptane jet under reactivity controlled compression ignition (RCCI) conditions are investigated using 2-D direct numerical simulation with a 116-species PRF reduced mechanism. For RCCI combustion, n-heptane and iso-octane are selected as two different fuels that have opposite ignition characteristics. In real engine, relatively-low reactivity fuel is delivered by port-fuel injection and relatively-high reactivity fuel is directly injected. Thus, the ignition characteristics of temporally evolving jet can be investigated with different jet velocity, U0. It is found that the first-stage ignition kernels occur within n-heptane jet near the mixing layer and develop into low temperature flame, propagating into relatively fuel-rich mixture of n-heptane jet. The high temperature ignition kernel is also formed in the nheptane jet, and then rapidly propagate into both relatively fuel-rich n-heptane jet and fuel-lean iso-octane/air mixture. Finally, the end-gas autoignition occurs. It is also found that the first- and second-stage ignitions occur quickly with increasing U0; the overall combustion is prolonged and the peak of heat release rate is reduced with increasing U0

DNSs of the Ignition of a Lean n-Heptane/Air Mixture under SCCI Conditions: Chemical Aspects

[No abstract available

A DNS study of ignition characteristics of a lean PRF/air mixture with CH2O and H2O2 addition under HCCI combustion-relevant conditions

The effects of additive injection including CH2O and H2O2 on the ignition characteristics of a lean pri-mary reference fuel (PRF)/air mixture under homogeneous-charge compression ignition (HCCI) combus-tion conditions are investigated using 2-D direct numerical simulations (DNSs) with a 116-species reduced chemical mechanism. The 2-D DNSs of HCCI combustion are performed by varying the type and amount of the additives with a pseudo-species model and a compression-heating/expansion-cooling model. It is found that the first-stage and main ignitions are retarded by CH2O addition while the latter is promoted by H2O2 addition. By adjusting the amounts of dual additives, the main ignition can be manipulated to occur at a specific time similar to that with no additives while its mean heat release rate becomes more distributed over time than that with no additives. Combustion mode analysis reveals that a mixed mode of combustion occurs during the late phase of HCCI combustion with CH2O addition or dual ad-ditives, while spontaneous ignition mode of combustion is predominant for cases with H2O2 addition or no additives. Displacement speed analysis also verifies that CH2O addition induces deflagration rather than spontaneous ignition at the reaction fronts, which consequently leads to a smooth ignition of the RPF/air mixture. In addition, chemical explosive mode analysis (CEMA) identifies important variables and elementary reactions for low-, intermediate-, and high-temperature chemistries for the ignition of PRF/air mixture with and without additives. (c) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved

Tìm hiểu văn học Hàn Quốc thế kỷ 20

203 tr. ; 21 cm