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排序方式: 共有177条查询结果,搜索用时 15 毫秒
111.
Rebecca J. Robbins Jadwiga Leonczak J. Christopher Johnson Julia Li Catherine Kwik-Uribe Ronald L. Prior Liwei Gu 《Journal of chromatography. A》2009,1216(24):4831-4840
The quantitative parameters and method performance for a normal-phase HPLC separation of flavanols and procyanidins in chocolate and cocoa-containing food products were optimized and assessed. Single laboratory method performance was examined over three months using three separate secondary standards. RSD(r) ranged from 1.9%, 4.5% to 9.0% for cocoa powder, liquor and chocolate samples containing 74.39, 15.47 and 1.87 mg/g flavanols and procyanidins, respectively. Accuracy was determined by comparison to the NIST Standard Reference Material 2384. Inter-lab assessment indicated that variability was quite low for seven different cocoa-containing samples, with a RSD(R) of less than 10% for the range of samples analyzed. 相似文献
112.
Diego Prior 《Annals of Operations Research》2006,145(1):281-299
This paper analyses hospital performance using Data Envelopment Analysis (DEA) and the Malmquist productivity index. We follow
two approaches to quantify movements in productivity: (1) the traditional approach that only considers output and input variables;
and (2) a more comprehensive approach that incorporates movements in quality and restricts some achievements, if quality is
reduced. On the premise that the indicator for quality (nosocomial infections) is equivalent to a bad output, we explore the characteristics of, and compare the results of, the different technological
ways to incorporate quality (good or bad attributes, strong or weak disposability technological assumptions). After discussing
the virtues and limitations of the existing possibilities, the paper presents a better formulation that allows the preservation
of TQM postulates. The decomposition in the Malmquist productivity index shows an improvement in productivity and a positive
technical change, especially when quality is introduced.
This paper forms part of a more extensive research work, financed by the Spanish Science and Technology Ministry (ref. SEC2003-047707). 相似文献
113.
DABCO‐functionalized polysulfones as anion‐exchange membranes for fuel cell applications: Effect of crosslinking
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María Teresa Pérez‐Prior Nieves Ureña Monika Tannenberg Carmen del Río Belén Levenfeld 《Journal of Polymer Science.Polymer Physics》2017,55(17):1326-1336
A series of DABCO‐functionalized polysulfones were synthesized and characterized. The effect that crosslinking has on the membrane properties containing different degrees of functionalization was evaluated. These polymers showed good thermal stability below the fuel cell operation temperature, T < 100 °C, reflected by the TOD, TFD, and thermal durability. The water uptake increased as the percentage of DABCO groups increased and the crosslinked membranes showed lower capacity to absorb water than the non‐crosslinked ones favoring thus the dimensional stability of the first ones. Membranes in the chloride form containing low degree of functionalization exhibited the highest tensile strength values. The ionic conductivity of non‐crosslinked membranes varied as a function of the functionalization degree until a value of around 100% achieving a maximum value at 86%. However, the crosslinked ones showed satisfactory ionic conductivities for values higher than 100%. The behavior of these polymeric materials in alkaline solutions revealed a great alkaline stability necessary to be used as solid electrolytes in fuel cells. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1326–1336 相似文献
114.
M. Demper W. Heimbrodt C. Bradford K. A. Prior 《Journal of nanoparticle research》2011,13(11):5635-5640
We used a sensitive optical method to study the magnetic phase transition of antiferromagnetic MnS layers. The method is applicable
for very small numbers of spins, e.g., thin single layers. We studied the optical and magnetic properties of MnS layers using
the internal optical transition of the manganese 3d-shell. The temperature dependence of the Mn-emission exhibits a pronounced minimum revealing the para- to anti-ferromagnetic
phase transition. The MnS layers were grown by molecular beam epitaxy, embedded between diamagnetic ZnSe cladding layers on
a (100)-GaAs substrate. It was found that the Néel-temperature itself is influenced by the biaxial strain and can be changed
in an external magnetic field in case of quasi 2D MnS-layers. The phase diagram reveals a weak Ising like anisotropic contribution
in case of a 1.8 nm thin layer, whereas a 8.6 nm thick layer behaves still like an ideal isotropic Heisenberg system. 相似文献
115.
Initial implementation of an electrodynamic ion funnel with fourier transform ion cyclotron resonance mass spectrometry 总被引:2,自引:0,他引:2
Belov ME Gorshkov MV Udseth HR Anderson GA Tolmachev AV Prior DC Harkewicz R Smith RD 《Journal of the American Society for Mass Spectrometry》2000,11(1):19-23
Fourier transform ion cyclotron resonance (FTICR) mass spectrometry has become a widely used method to study biopolymers. The method, in combination with an electrospray ionization (ESI) source has demonstrated the highest resolution and accuracy yet achieved for characterization of biomolecules and their noncovalent complexes. The most common design for the ESI interface includes a heated capillary inlet followed by a skimmer having a small orifice to limit gas conductance between a higher pressure (1 to 5 torr) source region and the lower pressure ion guide. The ion losses in the capillary-skimmer interface are large (estimated to be more than 90%) and thus reduce achievable sensitivity. In this work, we report on the initial implementation of a newly developed electrodynamic ion funnel in a 3.5 tesla ESI-FTICR mass spectrometer. The initial results show dramatically improved ion transmission as compared to the conventional capillary-skimmer arrangement. An estimated detection limit of 30 zeptomoles (approximately 18,000 molecules) has been achieved for the analysis of the proteins with molecular weights ranging from 8 to 20 kDa. 相似文献
116.
Maria João Ramalhosa Paula Paíga Simone Morais Cristina Delerue‐Matos Maria Beatriz Prior Pinto Oliveira 《Journal of separation science》2009,32(20):3529-3538
QuEChERS method was evaluated for extraction of 16 PAHs from fish samples. For a selective measurement of the compounds, extracts were analysed by LC with fluorescence detection. The overall analytical procedure was validated by systematic recovery experiments at three levels and by using the standard reference material SRM 2977 (mussel tissue). The targeted contaminants, except naphthalene and acenaphthene, were successfully extracted from SRM 2977 with recoveries ranging from 63.5–110.0% with variation coefficients not exceeding 8%. The optimum QuEChERS conditions were the following: 5 g of homogenised fish sample, 10 mL of ACN, agitation performed by vortex during 3 min. Quantification limits ranging from 0.12–1.90 ng/g wet weight (0.30–4.70 μg/L) were obtained. The optimized methodology was applied to assess the safety concerning PAHs contents of horse mackerel (Trachurus trachurus), chub mackerel (Scomber japonicus), sardine (Sardina pilchardus) and farmed seabass (Dicentrarchus labrax). Although benzo(a)pyrene, the marker used for evaluating the carcinogenic risk of PAHs in food, was not detected in the analysed samples (89 individuals corresponding to 27 homogenized samples), the overall mean concentration ranged from 2.52 ± 1.20 ng/g in horse mackerel to 14.6 ± 2.8 ng/g in farmed seabass. Significant differences were found between the mean PAHs concentrations of the four groups. 相似文献
117.
Free radicals and other reactive species are considered to be important causative factors in the development of diseases of aging such as cancer and cardiovascular diseases. This relationship has led to considerable interest in assessing the antioxidant capacity of foods and botanicals and other nutritional antioxidant supplements. The use of the oxygen radical absorbance capacity (ORAC) assay as a tool for antioxidant assessment is described and proposed as a method for comparing botanical sources and for standardizing nutritional supplements. The free radical or oxidant source is important and direct comparisons cannot be made between procedures that use different sources. The ORAC procedure uses 2,2'-azobis(2-amidinopropane) dihydrochloride as a peroxyl radical source, which is relevant to biological systems because the peroxyl radical is the most abundant free radical. Other oxidant sources (hydroxyl radical and Cu++) can also be used to characterize antioxidants in botanicals. Phenolics or polyphenolics are responsible for most of the antioxidant capacity in fruits, vegetables, and most botanical antioxidant supplements. Although little is known about the absorption and metabolism of these components, improvement in the in vivo antioxidant status has been observed in human subjects following consumption of antioxidant botanicals. The ORAC method provides a basis from which to establish appropriate dietary intakes that might impact health outcomes. 相似文献
118.
Jahnke T Weber T Landers AL Knapp A Schössler S Nickles J Kammer S Jagutzki O Schmidt L Czasch A Osipov T Arenholz E Young AT Díez Muiño R Rolles D García de Abajo FJ Fadley CS Van Hove MA Semenov SK Cherepkov NA Rösch J Prior MH Schmidt-Böcking H Cocke CL Dörner R 《Physical review letters》2002,88(7):073002
We have measured the angular distributions of 1s photoelectrons excited by circularly and linearly polarized light from fixed-in-space CO and N2 molecules, in the vicinity of their shape resonances. A strong circular dichroism, i.e., a strong dependence on the sense of rotation of the polarization vector of the photons, is found for both molecules. State-of-the-art one-electron multiple scattering and partially correlated random phase approximation calculations are in good agreement with many, but not all, aspects of the experimental data. 相似文献
119.
Juliana Albuquerque da Silva Lucas Guimarães Cardoso Denilson de Jesus Assis Gleice Valéria Pacheco Gomes Maria Beatriz Prior Pinto Oliveira Carolina Oliveira de Souza Janice Izabel Druzian 《Applied biochemistry and biotechnology》2018,186(3):750-763
This study aimed to evaluate the properties of xanthan gum produced by Xanthomonas campestris pv. campestris 1866 and 1867 from lignocellulosic agroindustrial wastes. XG was produced using an orbital shaker in a culture medium containing coconut shell (CS), cocoa husks (CH), or sucrose (S) minimally supplemented with urea and potassium. The XG production results varied between the CS, CH, and S means, and it was higher with the CH in strains 1866 (4.48 g L?1) and 1867 (3.89 g L?1). However, there was more apparent viscosity in the S gum (181.88 mPas) and the CS gum (112.06 mPas) for both 1866 and 1867, respectively. The ability of XGCS and XGCH to emulsify different vegetable oils was similar to the ability of XGS. All gums exhibited good thermal stability and marked groups in the elucidation of compounds and particles with rough surfaces. 相似文献
120.