排序方式: 共有11条查询结果,搜索用时 15 毫秒
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M. A. Addo J. K. Gbadago H. A. Affum T. Adom K. Ahmed G. M. Okley 《Journal of Radioanalytical and Nuclear Chemistry》2008,277(3):517-524
The concentration of thirty-four elements each in Ghanaian dried tobacco leaves and snuff (powdered tobacco) have been determined
using instrumental neutron activation analysis (INAA). The concentration of Hg, Cr, As and Cd in both set of samples were
found to be in excess of WHO limits for drinking water, thus indicating potential toxicity of the samples. Cr, Cd, Sb and
Cu were two to eight times high, whilst As and Hg were comparable in powdered tobacco and tobacco leaves. The aim of the study
was to determine the pattern of elemental concentrations and the toxicological strengths in both tobacco leaves and tobacco
powder. The results indicated that the toxicity of the snuff was higher than the tobacco. This indicated strongly that from
the medical point of view, the level of toxic accumulation in users might be potentially high in the tobacco powder compared
to the leaves. Thus, education of the Ghanaian public on the threshold value of toxic elements contained in both set of samples
was suggested to safeguard users against these addictives. 相似文献
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Analysis of a TE011 mode composite sapphire-rutile dielectric resonator has been carried out to study the temperature variation of resonance
frequency, close to the Cs atomic clock hyperfine frequency of 9.192 GHz. The complementary behavior of dielectric permittivity
with temperature of the composite has been exploited to obtain the desired turning point in the resonant frequency. The frequency
of the composite structure is found to be independent of the shield diameter beyond four times the puck diameter. 相似文献
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Philip Wiredu Addo Philip Ossowski Sarah MacPherson Andre E. Gravel Rajvinder Kaur Valerio Hoyos-Villegas Jaswinder Singh Valrie Orsat Marie-Jose Dumont Mark Lefsrud 《Molecules (Basel, Switzerland)》2022,27(5)
Pisum sativum is a leguminous crop suitable for cultivation worldwide. It is used as a forage or dried seed supplement in animal feed and, more recently, as a potential non-traditional oilseed. This study aimed to develop a low-cost, rapid, and non-destructive method for analyzing pea lipids with no chemical modifications that would prove superior to existing destructive solvent extraction methods. Different pea accession seed samples, prepared as either small portions (0.5 mm2) of endosperm or ground pea seed powder for comparison, were subjected to HR-MAS NMR analyses and whole seed samples underwent NIR analyses. The total lipid content ranged between 0.57–3.45% and 1.3–2.6% with NMR and NIR, respectively. Compared to traditional extraction with butanol, hexane-isopropanol, and petroleum ether, correlation coefficients were 0.77 (R2 = 0.60), 0.56 (R2 = 0.47), and 0.78 (R2 = 0.62), respectively. Correlation coefficients for NMR compared to traditional extraction increased to 0.97 (R2 = 0.99) with appropriate correction factors. PLS regression analyses confirmed the application of this technology for rapid lipid content determination, with trends fitting models often close to an R2 of 0.95. A better robust NIR quantification model can be developed by increasing the number of samples with more diversity. 相似文献
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MVN Murthy Urjit A Yajnik KRS Balaji G Bhattacharyya Amol Dighe Shashikant Dugad ND Hari Dass PK Kabir Kamales Kar D Indumathi John G Learned Debasish Majumdar NK Mondal MVN Murthy SN Nayak Sandip Pakvasa Amitava Raychaudhuri RS Raghavan G Rajasekaran R Ramachandran Alak K Ray Asim K Ray Saurabh Rindani HS Sharatchandra Rahul Sinha Nita Sinha S Umasankar Urjit A Yajnik 《Pramana》2000,55(1-2):347-355
We have identified some important and worthwhile physics opportunities with a possible neutrino detector located in India.
Particular emphasis is placed on the geographical advantage with a stress on the complimentary aspects with respect to other
neutrino detectors already in operation. 相似文献
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Erwin G. Abucayon Rahul L. Khade Douglas R. Powell Yong Zhang George B. Richter‐Addo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18771-18776
Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N2O. We previously reported that a heme Fe–NO model engages in this N?N bond‐forming reaction with NO. We now demonstrate that (OEP)CoII(NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX3 (X=F, C6F5) to generate N2O. DFT calculations support retention of the CoII oxidation state for the experimentally observed adduct (OEP)CoII(NO?BF3), the presumed hyponitrite intermediate (P.+)CoII(ONNO?BF3), and the porphyrin π‐radical cation by‐product of this reaction, and that the π‐radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous‐to‐ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO‐to‐N2O conversion reaction. 相似文献
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Gomez MA Jindal S Fletcher KM Foster LS Addo ND Valentin D Ghenoiu C Hamilton A 《The Journal of chemical physics》2007,126(19):194701
In the present paper, the authors focus on proton conduction pathways in a cubic perovskite KTaO(3) and an orthorhombic perovskite SrZrO(3). Density functional theory with a generalized gradient approximation is used to find proton binding sites. The nudged elastic band method is used to find transition states between minima. With this potential energy map of binding and transition states, adjacency matrices and their analogs identify four types of conduction paths in KTaO(3). Distortions from these paths are seen in SrZrO(3). In both cases, the lowest energy path has an intraoctahedral transfer rate-limiting barrier. A Fourier analysis of the OH stretch in ab initio molecular dynamics simulations revealed a strongly redshifted OH stretch in SrZrO(3) relative to KTaO(3). Hence, an orthorhombic system with a lowest energy conduction path limited by an intraoctahedral barrier can exhibit a redshifted OH stretch. 相似文献
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Effects of polymer wrapping and covalent functionalization on the stability of MWCNT in aqueous dispersions 总被引:1,自引:0,他引:1
Ntim SA Sae-Khow O Witzmann FA Mitra S 《Journal of colloid and interface science》2011,355(2):383-388
The colloidal behavior of aqueous dispersions of functionalized multiwall carbon nanotubes (F-CNTS) formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is presented. The presence of polymer on the nanotube surface provided steric stabilization, and the aggregation behavior of the colloidal system was quite different from its covalently functionalized analog. Based on hydrophobicity index, particle size distribution, zeta potential as well as the aggregation kinetics studied using time-resolved dynamic light scattering, the PVP wrapped CNT was somewhat less prone to agglomeration. However, its long-term stability was lower, and this was attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface. 相似文献