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排序方式: 共有169条查询结果,搜索用时 15 毫秒
1.
H. H. Mahmud A. Mansour F. M. Ezz-Eldin 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):261-272
Radiation indicator as well as radiation shielding of extremely high dose have been proposed. Three different types of a-SiO2 namely, G1-xerogel, G2-fused and G3-natural silica were monitored by EPR before and after γ-irradiation. The E′-center has been used for EPR radiation characterization of a-SiO2 with assuming that the signal intensity changes with γ-irradiation differently as those of other EPR signals do. Formation and decay of the E′-center are closely related with its precursor, diamagnetic oxygen vacancies. Gamma ray of large dose (500 kGy) creates oxygen vacancies giving up-and-down irradiation effects, which, therefore, might be useful for high dose radiation indicator (G1) and radiation shielding (G2 and G3). 相似文献
2.
Tahira Foyzun Abdullah Al Mahmud Md. Salim Ahammed Md. Imran Nur Manik Md. Kamrul Hasan KM Monirul Islam Simin Sobnom Lopa Md. Yusuf Al-Amin Kushal Biswas Mst. Rejina Afrin AHM Khurshid Alam Golam Sadik 《Molecules (Basel, Switzerland)》2022,27(3)
Neurotoxicity is a serious health problem of patients chronically exposed to arsenic. There is no specific treatment of this problem. Oxidative stress has been implicated in the pathological process of neurotoxicity. Polyphenolics have proven antioxidant activity, thereby offering protection against oxidative stress. In this study, we have isolated the polyphenolics from Acacia nilotica and investigated its effect against arsenic-induced neurotoxicity and oxidative stress in mice. Acacia nilotica polyphenolics prepared from column chromatography of the crude methanol extract using diaion resin contained a phenolic content of 452.185 ± 7.879 mg gallic acid equivalent/gm of sample and flavonoid content of 200.075 ± 0.755 mg catechin equivalent/gm of sample. The polyphenolics exhibited potent antioxidant activity with respect to free radical scavenging ability, total antioxidant activity and inhibition of lipid peroxidation. Administration of arsenic in mice showed a reduction of acetylcholinesterase activity in the brain which was counteracted by Acacia nilotica polyphenolics. Similarly, elevation of lipid peroxidation and depletion of glutathione in the brain of mice was effectively restored to normal level by Acacia nilotica polyphenolics. Gallic acid methyl ester, catechin and catechin-7-gallate were identified in the polyphenolics as the major active compounds. These results suggest that Acacia nilotica polyphenolics due to its strong antioxidant potential might be effective in the management of arsenic induced neurotoxicity. 相似文献
3.
D. Seweryniak P. J. Woods B. Blank M. P. Carpenter T. Davinson S. J. Freeman J. Grres A. Heinz R. V. F. Janssens H. Mahmud T. L. Khoo Z. Liu G. Mukherjee E. Rehm F. Sarazin J. Shergur M. Shawcross S. Sinha A. Woehr 《Physics letters. [Part B]》2004,590(3-4):170-175
The fusion–evaporation reaction 10B(12C, 2n) was used to make the first observation of in-beam γ decays from the astrophysically important nucleus 20Na, lying adjacent to the proton drip-line. All states below the proton threshold in 20Na were populated and identified in the experiment. These include new levels, previously unresolved levels, and states located with improved energy precision. The level structure of 20Na, and its γ transitions, are compared to the mirror partner 20F measured simultaneously in this experiment. In particular, a high degree of energy stability is found for all negative parity states. These results are discussed in the context of the nuclear shell model. 相似文献
4.
Michael A. Olatunji Mayeen U. Khandaker Ekramul H. N. M. Mahmud Yusoff Md. Amin Janet A. Ademola Deborah O. Olorode 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(3):933-945
Polypyrrole is incorporated with activated carbon in large size dopant solution and investigated for 137Cs removal studies. Adsorption experiments showed optimum conditions within 240 min contact time, pH 6, 0.2 g adsorbent and?≤?100 mg/l adsorbate dose, respectively, while the kinetic data followed pseudo-first-order model. Isotherm data were reproducible by the Langmuir isotherm yielding 23 mg/g maximum sorption capacity. Regeneration of adsorbent was attempted and indicated promising results within three cycles. The surface behavior has also been examined and revealed a well-ordered structure under gamma irradiation. This is a cheap adsorbent to consider and has also proven to possess higher sorption capacity than most highly-cost inorganic materials in use. 相似文献
5.
Coefficients of ergodicity and the scrambling index 总被引:1,自引:0,他引:1
Mahmud Akelbek 《Linear algebra and its applications》2009,430(4):1111-29
For a primitive stochastic matrix S, upper bounds on the second largest modulus of an eigenvalue of S are very important, because they determine the asymptotic rate of convergence of the sequence of powers of the corresponding matrix. In this paper, we introduce the definition of the scrambling index for a primitive digraph. The scrambling index of a primitive digraph D is the smallest positive integer k such that for every pair of vertices u and v, there is a vertex w such that we can get to w from u and v in D by directed walks of length k; it is denoted by k(D). We investigate the scrambling index for primitive digraphs, and give an upper bound on the scrambling index of a primitive digraph in terms of the order and the girth of the digraph. By doing so we provide an attainable upper bound on the second largest modulus of eigenvalues of a primitive matrix that make use of the scrambling index. 相似文献
6.
Mahnaz M.Abdi H.N.M.Ekramul Mahmud Luqman Chuah Abdullah Anuar Kassim Mohamad Zaki Ab.Rahman Josephine Liew Ying Chyi 《高分子科学》2012,(1):93-100
Electrical conductivity and optical properties of polypyrrole-chitosan(PPy-CHI) conducting polymer composites have been investigated to determine the optical transition characteristics and energy band gap of composite films.The two electrode method and I-V characteristic technique were used to measure the conductivity of the PPy-CHI thin films,and the optical band gap was obtained from their ultraviolet absorption edges.Depending upon experimental parameter,the optical band gap(Eg) was found within 1.30-2.32 eV as estimated from optical absorption data.The band gap of the composite films decreased as the CHI content increased.The room temperature electrical conductivity of PPy-CHI thin films was found in the range of 5.84×10-7-15.25×10-7 S·cm-1 depending on the chitosan content.The thermogravimetry analysis(TGA) showed that the CHI can improve the thermal stability of PPy-CHI composite films. 相似文献
7.
Asamizu S Xie P Brumsted CJ Flatt PM Mahmud T 《Journal of the American Chemical Society》2012,134(29):12219-12229
Sedoheptulose 7-phosphate cyclases are enzymes that utilize the pentose phosphate pathway intermediate, sedoheptulose 7-phosphate, to generate cyclic precursors of many bioactive natural products, such as the antidiabetic drug acarbose, the crop protectant validamycin, and the natural sunscreens mycosporine-like amino acids. These proteins are phylogenetically related to the dehydroquinate (DHQ) synthases from the shikimate pathway and are part of the more recently recognized superfamily of sugar phosphate cyclases, which includes DHQ synthases, aminoDHQ synthases, and 2-deoxy-scyllo-inosose synthases. Through genome mining and biochemical studies, we identified yet another subset of DHQS-like proteins in the actinomycete Actinosynnema mirum and the myxobacterium Stigmatella aurantiaca DW4/3-1. These enzymes catalyze the conversion of sedoheptulose 7-phosphate to 2-epi-valiolone, which is predicted to be an alternative precursor for aminocyclitol biosynthesis. Comparative bioinformatics and biochemical analyses of these proteins with 2-epi-5-epi-valiolone synthases (EEVS) and desmethyl-4-deoxygadusol synthases (DDGS) provided further insights into their genetic diversity, conserved amino acid sequences, and plausible catalytic mechanisms. The results further highlight the uniquely diverse DHQS-like sugar phosphate cyclases, which may provide new tools for chemoenzymatic, stereospecific synthesis of various cyclic molecules. 相似文献
8.
Mat Rasol Awang Hassan Hamdani Mutaat Mohd. Shukri Mahmud Wan Badrin Wan Husain Tajuddin Osman Khomsaton Abu Bakar Asmahwati Kassim Zal U''yun Wan Mahmud Ishak ManafTamikazu Kume Shoji Hashimoto 《Radiation Physics and Chemistry》1993,42(4-6):611-616
In solid state fermentation, Pleurotus sajor-caju has been found to be able to degrade at least 30% oil palm empty Fruit Bunch (EFB) fibre leaving 70 % useful materials. Conditions under which fermentation carried out were investigated. It was found that, in the temperature range between 25– 28 °C, relative ph between 6–8, moisture between 60–70 % and medium composition of CaCO3: rice bran 2 %: 5 % were the optimum conditions. The results showed in fermented products that, there were substantial reduction in cellulosic component such as Crude Fiber (CF, 18 %); Acid Detergent Fibre (ADF, 45 %), Neutral Detergent Fibre (NDF, 61 %) and Acid Detergent Lignin (ADL, 14 %). However, Crude Protein (CP, 10%) increased resulted from single cell protein enrichment of mycelial microbial mass. The mass reductions of substrate in fermentation process corresponds to the CO2 released during fermentation. Hence, attributable to the decreased in content of CF, ADF, NDF, and ADL. The digestibility study has also been carried out to determine the useful level of this product to ruminant. Aflatoxin content was detected low in both the initial substrates and products. Based on nutritional value and low content of aflatoxin, the product is useful as a source of roughage to ruminant. 相似文献
9.
M. U. Rajput Mahmud Ahmad Waqar Ahmad 《Journal of Radioanalytical and Nuclear Chemistry》2002,251(3):457-462
The characteristic absolute efficiency response curves of a high purity germanium detector (HPGe) for different counting geometries have been established in the energy range 50–1500 keV by measuring the absolute efficiencies using both mono-energetic and multi-gamma emitting radionuclide point calibrated sources supplied by IAEA. Several fitting functions proposed in the literature were assessed for interpolation within the intermediate energy range of interest. The values of the function parameters have been determined by using the linear least square methods. The problems associated with the measurements of experimental efficiency data at small source–detector distances and the importance of the correlation matrix in the estimation of precise uncertainties have been shown. It was found that the inclusion of correlation matrices in the propagation of error formulae plays a significant role up to 450 keV gamma-ray energy and results in a drastic reduction of errors associated with the predicted efficiencies. The discrepancy at closer counting geometries in the absence of true gamma-gamma coincidence corrections is found to reach to about 30%. 相似文献
10.
Feedback control on thermal convection in a fluid-saturated porous medium is investigated based on the dynamical systems approach.
A low dimensional Lorenz-like model was obtained using the Galerkin-truncated approximation. The possible suppression or enhancement
of chaotic convection is demonstrated when the fluid layer is subjected to feedback control in a low-dimensional framework. 相似文献