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61.
Willem de Haan Yolande AL Pijnenburg Rob LM Strijers Yolande van der Made Wiesje M van der Flier Philip Scheltens Cornelis J Stam 《BMC neuroscience》2009,10(1):101-12
Background
Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks. 相似文献62.
63.
Influence of Support Type and Metal Loading in Methane Decomposition over Iron Catalyst for Hydrogen Production
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Ahmed A. Ibrahim Ahmed S. Al‐Fatesh Wasim U. Khan Mostafa A. Soliman Raja L. AL Otaibi Anis H. Fakeeha 《中国化学会会志》2015,62(7):592-599
Natural gas resources, stimulate the method of catalytic methane decomposition. Hydrogen is a superb energy carrier and integral component of the present energy systems, while carbon nanotubes exhibit remarkable chemical and physical properties. The reaction was run at 700 °C in a fixed bed reactor. Catalyst calcination and reduction were done at 500 °C. MgO, TiO2 and Al2O3 supported catalysts were prepared using a co‐precipitation method. Catalysts of different iron loadings were characterized with BET, TGA, XRD, H2‐TPR and TEM. The catalyst characterization revealed the formation of multi‐walled nanotubes. Alternatively, time on stream tests of supported catalyst at 700 °C revealed the relative profiles of methane conversions increased as the %Fe loading was increased. Higher %Fe loadings decreased surface area of the catalyst. Iron catalyst supported with Al2O3 exhibited somewhat higher catalytic activity compared with MgO and TiO2 supported catalysts when above 35% Fe loading was used. CH4 conversion of 69% was obtained utilizing 60% Fe/Al2O3 catalyst. Alternatively, Fe/MgO catalysts gave the highest initial conversions when iron loading below 30% was employed. Indeed, catalysts with 15% Fe/MgO gave 63% conversion and good stability for 1 h time on stream. Inappropriateness of Fe/TiO2 catalysts in the catalytic methane decomposition was observed. 相似文献
64.
Functionalized nanoparticles based solid‐phase membrane micro‐tip extraction and high‐performance liquid chromatography analyses of vitamin B complex in human plasma
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Imran Ali Umma Kulsum Zeid A. AL‐Othman Abdulrahman Alwarthan Kishwar Saleem 《Journal of separation science》2016,39(14):2678-2688
Iron nanoparticles were prepared by a green method following functionalization using 1‐butyl‐3‐methylimidazolium bromide. 1‐Butyl‐3‐methylimidazole iron nanoparticles were characterized using FTIR spectroscopy, energy dispersive X‐ray fluorescence, X‐ray diffraction, scanning electron microscopy and transmission electron microscopy. The nanoparticles were used in solid‐phase membrane micro‐tip extraction to separate vitamin B complex from plasma before high‐performance liquid chromatography. The optimum conditions obtained were sorbent (15 mg), agitation time (30 min), pH (9.0), desorbing solvent [water (5 mL) + methanol (5 mL) + sodium hydroxide (0.1 N) + acetic acid (d = 1.05 kg/L, pH 5.5), desorbing volume (10 mL) and desorption time (30 min). The percentage recoveries of all the eight vitamin B complex were from 60 to 83%. A high‐performance liquid chromatography method was developed using a PhE column (250 × 4.6 mm, 5.0 μm) and water/acetonitrile (95:5, v/v; pH 4.0 with 0.1% formic acid) mobile phase. The flow rate was 1.0 mL/min with detection at 270 and 210 nm. The values of the capacity, separation and resolution factor were 0.57–39.47, 1.12–6.00 and 1.84–26.26, respectively. The developed sample preparation and chromatographic methods were fast, selective, inexpensive, economic and reproducible. The developed method can be applied for analyzing these drugs in biological and environmental matrices. 相似文献
65.
Ultra high performance liquid chromatography with mass spectrometry method for the simultaneous determination of phenolic constituents in honey from various floral sources using multiwalled carbon nanotubes as extraction sorbents
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Saikh Mohammad Wabaidur Yacine Badjah Hadj Ahmed Munir Saeed Obbed Nasser Mohamed AL‐Harbi Turki Mohammad AL‐Turki 《Journal of separation science》2015,38(15):2597-2606
An ultra high performance liquid chromatography with mass spectrometry method has been developed for the simultaneous separation, identification and determination of 22 phenolic constituents in honey from various floral sources from Yemen. Solid‐phase extraction was used for extraction of the target phenolic constituents from honey samples, while multiwalled carbon nanotubes were used as solid‐phase adsorbent. The chromatographic separation of all phenolic constituents was performed on a BEH C18 column using a linear gradient elution with a binary mobile phase mixture of aqueous 0.1% formic acid and methanol. The quantitation was carried out in selected ion reaction monitoring acquisition mode. The total amount of phenolic acids, flavonoids and other phenols in each analyzed honey was found in the range of 338–3312, 122–5482 and 2.4–1342 μg/100 g of honey, respectively. 4‐Hydroxybenzoic acid was found to be the major phenolic acid. The main detected flavonoid was chrysin, while cinnamic acid was found to be the major other phenol compound. The regeneration of solid phase adsorbent to be reused and recovery results confirm that the proposed method could be potentially used for the routine analysis of phenolic constituents in honey extract. 相似文献
66.
Paper has been present in the world of analytical chemistry for centuries, but it seems that just a few years back it was rediscovered as a valuable substrate for sensors. We can easily list some of the countless advantages of this simple cellulosic substrate, including mechanical properties, three-dimensional fibrous structure, biocompatibility and biodegradability, easiness of production and modification, reasonable price, and availability all over the world. Those characteristics make paper a first-choice substrate for disposable sensors and integrated sensing platforms. Nowadays, numerous examples of paper-based sensors are being presented in the literature. This review describes some of the most prominent examples classifying them by type of detection: optical (colorimetric, fluorescence, surface-enhanced Raman spectroscopy, and transmittance methods) and electrochemical (voltammetric, potentiometric, and conductivity-based methods). We take a closer look at recent advances in immunoassays fabricated on paper, excluding simple lateral flow tests assembled on nitrocellulose. This review also summarizes the main advantages and disadvantages of the use of paper as a substrate for sensors, as well as its impact on their performance and application, presents a short history of paper in analytical chemistry, and discusses fabrication methods and available sources of paper. 相似文献
67.
68.
A simple procedure is proposed which yields, from carbon-13 longitudinal relaxation times and nuclear Overhauser enhancements, information concerning the local mobility of a given CH vector in an alkyi chain. This method is based on the definition of an effective rotation axis related to internal motions and makes use of Woessner's equations. It yields a correlation time τR characteristic of the overall reorientation. In addition, for each carbon Ci a correlation time τGi, associated with the fast motion of the CiH vector, and an angle θi, between CiH and an effective rotation axis, are determined. The effect of cross-correlation spectral densities is discussed. This model is used for analysing relaxation data of decylammonium chloride micelles. It is further checked by interpreting experimental results at two different observation frequencies. 相似文献
69.
In order to complete the rs structure of chlorobenzene given in a preceding paper, a variety of isotopic species of this molecule were synthesized and their microwave spectra studied. This made twenty isotopic species available, enabling the determination of the geometrical parameters by a least squares method. Fitting only differences of moments of inertia either for monosubstituted species or to multiply substituted species gave the same result. They hardly differ from the ro values and agree with the rs values obtained by the Kraitchman equations. The resulting error limits were reduced, however.
The following structural parameters were obtained, C1C2 = 1.399 Å, C2C3 = 1.386 Å, C3C4 = 1.3976 Å, C1Cl = 1.7248 Å, C2H2 = 1.080 Å, C3H3 = 1.081 Å, C4H4 = 1.081 Å, C6C1C2 = 120° 16, C1C2C3 = 119°78, C2C3C4 = 120°24, C3C4C5 = 119°80, C1C2H2 = 119°45, C2C3H3 = 119°76.
The structure of the ring differs significantly from C6 symmetry. The deformation can be regarded as a compression of the position C1 while the angle of C2H2 bond is also changed. 相似文献
70.