Nonequilibrium nuclear-electron spin dynamics in semiconductor quantum dots

We study the spin dynamics in charged quantum dots in the situation where the resident electron is coupled to only about 200 nuclear spins and where the electron spin splitting induced by the Overhauser field does not exceed markedly the spectral broadening. The formation of a dynamical nuclear polarization as well as its subsequent decay by the dipole-dipole interaction is directly resolved in time. Because not limited by intrinsic nonlinearities, almost complete nuclear polarization is achieved, even at elevated temperatures. The data suggest a nonequilibrium mode of nuclear polarization, distinctly different from the spin temperature concept exploited on bulk semiconductorsComment: 5 pages, 4 figure

Phenytoin Interaction with Enteral Feedings Administered through Nasogastric Tubes

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142072/1/jpen0513.pd

Evaluation of water-repellent properties of cements according to wettability method

Оцінено існуючі методики визначення гідрофобних властивостей цементів, вказано переваги та недоліки їх застосування. Запропоновано оцінювати гідрофобність дисперсних цементів за методиками визначення крайових кутів змочування та показників змочуваності. Виявлено переваги і недоліки методик та наведено рекомендації щодо доцільності їх застосування. Дослідження крайового кута змочування на поверхні дисперсного матеріалу або пресованих таблеток доцільно застосовувати, якщо цемент містить гідрофобну добавку. Дослідження змочуваності доцільно виконувати, якщо цемент містить гідрофобізуючу добавку. Обидві методики дозволяють визначити оптимальні концентрації добавок та порівнювати дію різних добавок на властивості цементів. Ключові слова: гідрофобний цемент, методика, крайовий кут змочування, капілярне підняття, рівняння Уошборнаcandidate of engineering science, associated professor Tokarchuk V. V., Pryhozha H. V., Fleisher H. U. Evaluation of water-repellent properties of cements according to wettability method / National Technical University of Ukraine “Kyiv Polytechnic Institute”, Ukraine, KyivMethods of cement water-repellent properties are evaluated, advantages and disadvantages of their utilization are described. Evaluation of cement water-repellent properties according to methods of contact angle and wettability is proposed.  Benefits and drawbacks of methods and guidelines of their utilization are given. The method of contact angle should be used if the cement is treated with water-repellent admixtures. The method of wettability should be used if the cement is treated with waterproofing admixtures. Both methods make possible to determine effective concentrations and compare different admixtures. Key words: hydrophobic cement, method, contact angle, capillary ascension, Washburn’s equatio

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Absolute ¹³C/¹²C isotope amount ratio for Vienna PeeDee Belemnite from infrared absorption spectroscopy

Measurements of isotope ratios are predominantly made with reference to standard specimens that have been characterized in the past. In the 1950s, the carbon isotope ratio was referenced to a belemnite sample collected by Heinz Lowenstam and Harold Urey in South Carolina’s PeeDee region. Due to exhaustion of the sample since then, reference materials that are traceable to the original artefact are used to define the Vienna PeeDee Belemnite scale for stable carbon isotope analysis. However, these reference materials have also become exhausted or proven to exhibit unstable composition over time, mirroring issues with the international prototype of the kilogram that led to a revised International System of Units. A campaign to elucidate the stable carbon isotope ratio of Vienna PeeDee Belemnite is underway, but independent measurement techniques are required to support it. Here we report an accurate value for the stable carbon isotope ratio inferred from infrared absorption spectroscopy, fulfilling the promise of this fundamentally accurate approach. Our results agree with a value recently derived from mass spectrometry and therefore advance the prospects of International System of Units–traceable isotope analysis. Further, our calibration-free method could improve mass balance calculations and enhance isotopic tracer studies in carbon dioxide source apportionment

Acetic Acid Aldol Reactions in the Presence of Trimethylsilyl Trifluoromethanesulfonate

In the presence of TMSOTf and a trialkylamine base, acetic acid undergoes aldol addition to non-enolizable aldehydes under exceptionally mild conditions. Acidic workup yields the β-hydroxy carboxylic acid. The reaction appears to proceed via a three-step, one-pot process, including in situ trimethylsilyl ester formation, bis-silyl ketene acetal formation, and TMSOTf-catalyzed Mukaiyama aldol addition. Independently synthesized TMSOAc also undergoes aldol additions under similar conditions

Effect of Phosphorus Nutrition on Growth and Physiology of Cotton Under Ambient and Elevated Carbon Dioxide

Phosphorous deficiency in soil limits crop growth and productivity in the majority of arable lands worldwide and may moderate the growth enhancement effect of rising atmospheric carbon dioxide (CO2) concentration. To evaluate the interactive effect of these two factors on cotton (Gossypium hirsutum) growth and physiology, plants were grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.20, 0.05 and 0.01 mM) under ambient and elevated (400 and 800 μmol mol‒1, respectively) CO2. Phosphate stress caused stunted growth and resulted in early leaf senescence with severely decreased leaf area and photosynthesis. Phosphate stress led to over 77 % reduction in total biomass across CO2 levels. There was a below-ground (roots) shift in biomass partitioning under Pi deficiency. While tissue phosphorus (P) decreased, tissue nitrogen (N) content tended to increase under Pi deficiency. The CO2 × Pi interactions were significant on leaf area, photosynthesis and biomass accumulation. The stimulatory effect of elevated CO2 on growth and photosynthesis was reduced or highly depressed suggesting an increased sensitivity of cotton to Pi deficiency under elevated CO2. Although, tissue P and stomatal conductance were lower at elevated CO2, these did not appear to be the main causes of cotton unresponsiveness to elevated CO2 under severe Pi-stress. The alteration in the uptake and utilization of N was suggested due to a consistent reduction (18–21 %) in the cotton plant tissue N content under elevated CO2

Modeling drug release from dynamically swelling poly(hydroxyethyl methacrylate-co-methacrylic acid) hydrogels

Drug release from a swelling hydrogel matrix is a complicated process where diffusion of drug molecules is coupled to the swelling kinetics. The swelling influences the diffusional flux of drug molecules by increasing the diffusion coefficient and diffusional pathlength. Release of phenylpropanolamine from a poly(hydroxyethyl methacrylate-co-methacrylic acid) hydrogel, initially at low pH, is highly influenced by swelling in a neutral pH medium. Swelling in these ionizing gels is a very long process, even in the absence of a glassy core, indicating that the swelling is not a simple Fickian process. In this paper, a novel approach is introduced to model the phenylpropanolamine release from these swelling gels. Through a free volume relationship, the experimentally determined swelling kinetics are coupled to a diffusion mechanism for the drug molecules. This model was shown to give an accurate prediction of phenylpropanolamine release from poly(hydroxyethyl methacrylate-co-methacrylic acid) gels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28600/1/0000408.pd