115 research outputs found
Cod Liver Oil as a Source of Vitamin A
In the course of experiments having for their object the study of the properties of vitamin A with a view to its isolation, certain observations were made concerning the behavior of animals on various rations containing cod liver oil. It was noted that different samples of cod liver oil apparently vary markedly in vitamin A potency. Xerophthalmia has been produced in rats on diets containing as much as 3 per cent of cod liver oil. Synthetic rations containing cod liver oil evolve a penetrating odor resembling acrolein. When the cod liver oil is replaced with butter fat, this odor is not observed. It is possible that the failure of rats on diets containing certain samples of cod liver oil may be due to one or more of the following factors. 1. A decreased consumption of the diet clue to this decomposition product. 2. A destruction of vitamin A which runs parallel with the destruction of the cod liver oil. 3. Certain samples of cod liver oil are not as rich in vitamin A as supposed heretofore
CoQ10 Deficient Endothelial Cell Culture Model for the Investigation of CoQ10 BloodâBrain Barrier Transport
Primary coenzyme Q10 (CoQ10) deficiency is unique among mitochondrial respiratory chain disorders in that it is potentially treatable if high-dose CoQ10 supplements are given in the early stages of the disease.While supplements improve peripheral abnormalities, neurological symptoms are only partially or temporarily ameliorated. The reasons for this refractory response to CoQ10 supplementation are unclear, however, a contributory factor may be the poor transfer of CoQ10 across the bloodâbrain barrier (BBB). The aim of this study was to investigate mechanisms of CoQ10 transport across the BBB, using normal and pathophysiological (CoQ10 deficient) cell culture models. The study identifies lipoprotein-associated CoQ10 transcytosis in both directions across the in vitro BBB. Uptake via SR-B1 (Scavenger Receptor) and RAGE (Receptor for Advanced Glycation Endproducts), is matched by efflux via LDLR (Low Density Lipoprotein Receptor) transporters, resulting in no ânetâ transport across the BBB. In the CoQ10 deficient model, BBB tight junctions were disrupted and CoQ10 ânetâ transport to the brain side increased. The addition of anti-oxidants did not improve CoQ10 uptake to the brain side. This study is the first to generate in vitro BBB endothelial cell models of CoQ10 deficiency, and the first to identify lipoprotein-associated uptake and efflux mechanisms regulating CoQ10 distribution across the BBB. The results imply that the uptake of exogenous CoQ10 into the brain might be improved by the administration of LDLR inhibitors, or by interventions to stimulate luminal activity of SR-B1 transporters
Bright triplet excitons in lead halide perovskites
Nanostructured semiconductors emit light from electronic states known as
excitons[1]. According to Hund's rules[2], the lowest energy exciton in organic
materials should be a poorly emitting triplet state. Analogously, the lowest
exciton level in all known inorganic semiconductors is believed to be optically
inactive. These 'dark' excitons (into which the system can relax) hinder
light-emitting devices based on semiconductor nanostructures. While strategies
to diminish their influence have been developed[3-5], no materials have been
identified in which the lowest exciton is bright. Here we show that the lowest
exciton in quasi-cubic lead halide perovskites is optically active. We first
use the effective-mass model and group theory to explore this possibility,
which can occur when the strong spin-orbit coupling in the perovskite
conduction band is combined with the Rashba effect [6-10]. We then apply our
model to CsPbX3 (X=Cl,Br,I) nanocrystals[11], for which we measure size- and
composition-dependent fluorescence at the single-nanocrystal level. The bright
character of the lowest exciton immediately explains the anomalous
photon-emission rates of these materials, which emit 20 and 1,000 times
faster[12] than any other semiconductor nanocrystal at room[13-16] and
cryogenic[17] temperatures, respectively. The bright exciton is further
confirmed by detailed analysis of the fine structure in low-temperature
fluorescence spectra. For semiconductor nanocrystals[18], which are already
used in lighting[19,20], lasers[21,22], and displays[23], these optically
active excitons can lead to materials with brighter emission and enhanced
absorption. More generally, our results provide criteria for identifying other
semiconductors exhibiting bright excitons with potentially broad implications
for optoelectronic devices.Comment: 14 pages and 3 figures in the main text, Methods and extended data 16
pages which include 11 figures, and supporting information 28 page
Bright triplet excitons in caesium lead halide perovskites
Nanostructured semiconductors emit light from electronic states known as excitons. For organic materials, Hundâs rules state that the lowest-energy exciton is a poorly emitting triplet state. For inorganic semiconductors, similar rules predict an analogue of this triplet state known as the âdark excitonâ. Because dark excitons release photons slowly, hindering emission from inorganic nanostructures, materials that disobey these rules have been sought. However, despite considerable experimental and theoretical efforts, no inorganic semiconductors have been identified in which the lowest exciton is bright. Here we show that the lowest exciton in caesium lead halide perovskites (CsPbX_3, with Xâ=âCl, Br or I) involves a highly emissive triplet state. We first use an effective-mass model and group theory to demonstrate the possibility of such a state existing, which can occur when the strong spinâorbit coupling in the conduction band of a perovskite is combined with the Rashba effect. We then apply our model to CsPbX_3 nanocrystals, and measure size- and composition-dependent fluorescence at the single-nanocrystal level. The bright triplet character of the lowest exciton explains the anomalous photon-emission rates of these materials, which emit about 20 and 1,000 times faster than any other semiconductor nanocrystal at room and cryogenic temperatures, respectively. The existence of this bright triplet exciton is further confirmed by analysis of the fine structure in low-temperature fluorescence spectra. For semiconductor nanocrystals, which are already used in lighting, lasers and displays, these excitons could lead to materials with brighter emission. More generally, our results provide criteria for identifying other semiconductors that exhibit bright excitons, with potential implications for optoelectronic devices
A 3D insight on the catalytic nanostructuration of few-layer graphene
The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting
Computer-aided detection in full-field digital mammography in a clinical population: performance of radiologist and technologists
Alicyclic Syntheses. III. The DielsâAlder Reaction with Alkylmercaptotoluquinones. A Synthesis of trans-9-Methyl-â” 6
Caffeine consumption and methotrexate dosing requirement in psoriasis and psoriatic arthritis
The effect of low concentrations of carbofuran, choline salt of maleic hydrazine, propham and chlorpropham on sister-chromatid exchanges (SCE) frequency in human lymphocytes in vitro
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