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41.
Dr. Saeed Chashmniam Dr. João M. C. Teixeira Prof. Juan Carlos Paniagua Prof. Miquel Pons 《Chembiochem : a European journal of chemical biology》2021,22(6):1001-1004
Coupling of side chain dynamics over long distances is an important component of allostery. Methionine side chains show the largest intrinsic flexibility among methyl-containing residues but the actual degree of conformational averaging depends on the proximity and mobility of neighboring residues. The 13C NMR chemical shifts of the methyl groups of methionine residues located at long distances in the same protein show a similar scaling with respect to the values predicted from the static X-ray structure by quantum methods. This results in a good linear correlation between calculated and observed chemical shifts. The slope is protein dependent and ranges from zero for the highly flexible calmodulin to 0.7 for the much more rigid calcineurin catalytic domain. The linear correlation is indicative of a similar level of side-chain conformational averaging over long distances, and the slope of the correlation line can be interpreted as an order parameter of the global side-chain flexibility. 相似文献
42.
Neville R. Moody Steven L. Robinson James P. Lucas James Handrock Robert Q. Hwang 《Journal of the American Ceramic Society》1995,78(1):114-120
In this study, short bar fracture toughness samples were used to determine the effects of radiation and hydrogen on the resistance to fracture of vitreous silica and four commercial borosilicate glasses. The results showed that neither exposure to 1010 rads of γ-radiation nor saturation to a room-temperature-equivalent exposure of 408 atm of hydrogen had an effect on fracture resistance. Nevertheless, when samples were saturated with hydrogen and then exposed to radiation, resistance to fracture increased significantly in some of the glasses. The increase in the resistance to fracture correlated directly with the increase in concentration of hydroxyl and hydride groups created by exposure to radiation and hydrogen. The concentration of these groups differs with glass composition and accounts for the difference in behavior between the types of glass studied. 相似文献
43.
44.
The axial mixing of ion exchange resin and liquid in fluidized beds is modelled by a series of well-mixed cells for the resin and an equal or larger number of mixed cells for the liquid. Concentration breakthrough curves are calculated using this mixing model, assuming finite mass transfer kinetics and irreversible equilibrium. The model is used to describe mixing patterns and kinetics in static fluidized beds (no resin flow); the information so obtained can be used to design continuous and periodic flow counter-current fluidized bed ion exchange systems. 相似文献
45.
A.C.S.F. Santos S. Damyanova G.N.R. Teixeira L.V. Mattos F.B. Noronha F.B. Passos J.M.C. Bueno 《Applied Catalysis A: General》2005,290(1-2):123-132
The effect of CeO2 loading (1–20 wt.%) on the properties and catalytic behaviors of CeO2–Al2O3-supported Pt catalysts on the partial oxidation of methane was studied. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and oxygen storage capacity (OSC). XRD and TPR results showed that the pretreatment temperature of the support influences on the amount of CeO2 with fluorite structure. The pretreatment temperature of the support and CeO2 loading influenced the morphology of Pt. OSC analysis showed a significant increase in the oxygen storage capacity per weight of CeO2 for samples with high CeO2 loading (12 and 20 wt.%). TPR analyses showed that the addition of Pt promotes the reduction of CeO2. This effect was more significant for the catalysts with high CeO2 loading (≥12 wt.%). The dispersion of Pt, measured by the rate of cyclohexane dehydrogenation, increases with increasing of the pretreatment temperature of the support. It was shown that the kind of the support is very important for obtaining of catalysts resistant to carbon formation. The catalysts with high CeO2 loading (≥12 wt.%) showed the highest catalytic activity and stability in the reaction of partial oxidation of methane due to a higher Pt–CeO2 interface. 相似文献
46.
Joseph C. McBride Xiaopeng Zhao Nancy B. Munro Charles D. Smith Gregory A. Jicha Lee Hively Lucas S. Broster Frederick A. Schmitt Richard J. Kryscio Yang Jiang 《Computer methods and programs in biomedicine》2014
Amnestic mild cognitive impairment (aMCI) often is an early stage of Alzheimer's disease (AD). MCI is characterized by cognitive decline departing from normal cognitive aging but that does not significantly interfere with daily activities. This study explores the potential of scalp EEG for early detection of alterations from cognitively normal status of older adults signifying MCI and AD. Resting 32-channel EEG records from 48 age-matched participants (mean age 75.7 years)—15 normal controls (NC), 16 early MCI, and 17 early stage AD—are examined. Regional spectral and complexity features are computed and used in a support vector machine model to discriminate between groups. Analyses based on three-way classifications demonstrate overall discrimination accuracies of 83.3%, 85.4%, and 79.2% for resting eyes open, counting eyes closed, and resting eyes closed protocols, respectively. These results demonstrate the great promise for scalp EEG spectral and complexity features as noninvasive biomarkers for detection of MCI and early AD. 相似文献
47.
As a renewable feedstock and due to its high functionality glycerol is an attractive reactant for the production of a large number of valuable compounds. We report on an environmentally friendly alternative to produce chemicals from the glycerol oxidation, which are currently produced either by stoichiometric oxidation processes or by enzymatic routes. We investigate the heterogeneously catalyzed liquid-phase oxidation of glycerol with carbon supported gold catalysts. The prepared nanosized gold catalysts are highly active, so that the reaction could be performed under atmospheric pressure. The influence of the preparation method of the catalysts has been investigated. Moreover, the support effect on the catalytic process has been studied and discussed in terms of pore structure of the investigated carbon materials. The promotor effect of platinum on Au/C catalysts was examined and it could be shown that the presence of Pt increases not only the catalyst activity but also the selectivity. By promoting the gold catalysts with platinum the selectivity to dihydroxyacetone could be increased from 26% (Au/C) to 36% (Au–Pt/C). 相似文献
48.
49.
S. Lucas E. Gonzlez M.P. Calvo C. Palencia E. Alonso M.J. Cocero 《The Journal of Supercritical Fluids》2007,40(3):462-469
Supercritical impregnation of Radiata pine with ethyl acetate and decanal using CO2 as carrier solvent has been studied at pilot plant scale. Radiata pine is one of the most common wood species that is originally from Australia and is widely grown in Spain and Portugal and ethyl acetate and decanal were selected as organic compounds.Some experiences were carried out to obtain the optimal operating conditions for the supercritical impregnation process. Experiments were conducted at pressures of 7–15 MPa, temperatures of 35–50 °C and solvent flow rate between 1.5 and 3.5 kg/h. The results of this study have indicated that the treatment gives much better preservative penetration and retention operating with low pressures (7.5 MPa), low temperatures (close to 35 °C) and moderate CO2 flow rate (3.5 kg/h) in the selected operating range. Moreover, a simple mathematical model of two adjustable parameters (external mass transfer coefficient and partition coefficient) has demonstrated to fit the experimental impregnation curves with reasonable accuracy (average absolute deviation, 3–10%). 相似文献
50.
A.?de?Lucas J.?Rincón I.?GraciaEmail author 《Journal of the American Oil Chemists' Society》2003,80(2):181-188
Supercritical CO2 extraction is a viable alternative process for the extraction of high-quality oil from olive husk (also known as olive pomace),
a residue obtained in the production of olive oil. We analyzed the effect of pressure (100–300 bar), temperature (40–60°C),
solvent flow (1–1.5 L/min), and particle size (0.30–0.55 mm) on four important quality parameters of the oil extracted with
CO2: tocopherol concentration, extinction coefficients at 232 and 270 nm, and saponification value. Response surface methodology
was used to obtain mathematical expressions related to the operating variables and parameters studied. Results from these
experiments were also used to design a three-step sequential CO2 extraction procedure to obtain a higher-quality extract. The optimal operational sequence consisted of a first extraction
step at 75 bar for 1 h using 1% (vol/vol) ethanol modifier, followed by a second extraction stage at 350 bar for 2.5 h without
ethanol and a third step, also at 350 bar, for 2.5 h but using ethanol. These extraction conditions obtained an intermediate
fraction of oil with 64% yield and all normal parameters according to European Commission food legislation. This fraction
is suitable without any further refining. On the contrary, the oils obtained by hexane extraction and by conventional supercritical
CO2 extraction at optimal conditions are suitable for human consumption after further refining. This last finding may result
in improved economics of the sequential CO2 extraction process compared to the conventional extraction method with hexane. 相似文献