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21.
ac Conductivity measurements are carried out across the metal to insulator transition in NiAl0.7Cr0.7Fe0.6O4. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling
behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency
conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime. 相似文献
22.
Novel sample treatment procedures for the determination of phosphorus in Cu‐based alloys using X‐ray fluorescence spectrometry to solve the microstructural effect issue
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Tadeusz Gorewoda Zofia Mzyk Jacek Anyszkiewicz Katarzyna Bilewska Andrzej Cybulski Szymon Malara Joanna Gołębiewska‐Kurzawska Magdalena Knapik Justyna Kostrzewa Magdalena Grzegorczyk 《X射线光谱测定》2017,46(6):554-562
The accurate analysis of hard CuP and CuPAg‐type solders using X‐ray fluorescence spectrometry is a difficult task. Surface milling, the most common sample preparation method for calibration materials, results in poor accuracy for the phosphorus analysis, as evidenced by the unacceptable values of the root mean square error. Meanwhile, the analysis of real samples provides incorrect results, and microstructural effects are the main source of error. Thus, this effect was negated by considering the information depth of the phosphorus Kα line and the microstructure size of the alloys. Phosphorus was measured using a thin layer of the sample (a thickness of several micrometers). As a result, the analyzed layer was a poor representative of the sample. Two different approaches for solving the microstructural effect issue were proposed. In the first method, the alloy was remelted under controlled conditions to obtain fine‐grain samples, which successfully limited the microstructural effects. The second solution used specially prepared thin layer samples, and the sample dissolution eliminated the microstructural effect. Using the developed sample treatment methods resulted in an improvement in the accuracy of the phosphorus calibration curves. This allowed for the correct determination of phosphorus and other alloying elements in the Cu‐based alloys with low uncertainties. 相似文献
23.
DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements
have been reported for the Co1.1−x
Zn
x
Ge0.1Fe1.2O1 spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic
ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained
under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important
role of magnetic anisotropy (due to the presence of Co2+ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed. 相似文献
24.
A. van de Riet H. Vonk Xu Xiaoding E. Otten A. Cybulski A. Stankiewicz R. Edvinsson J. A. Moulijn 《Reaction Kinetics and Catalysis Letters》1997,60(2):339-349
A series of Ni on alumina washcoated monoliths has been prepared and characterized. The selective liquid-phase hydrogenation
of benzaldehyde to benzyl alcohol in a Berty reactor has been used as a test reaction. 相似文献
25.
Cybulski H Krems RV Sadeghpour HR Dalgarno A Kłos J Groenenboom GC van der Avoird A Zgid D Chałasiński G 《The Journal of chemical physics》2005,122(9):094307
A detailed analysis of the He-NH((3)Sigma(-)) van der Waals complex is presented. We discuss ab initio calculations of the potential energy surface and fitting procedures with relevance to cold collisions, and we present accurate calculations of bound energy levels of the triatomic complex as well as collisional properties of NH molecules in a buffer gas of (3)He. The influence of the external magnetic field used to trap the NH molecules and the effect of the atom-molecule interaction potential on the collisionally induced Zeeman relaxation are explored. It is shown that minute variations of the interaction potential due to different fitting procedures may alter the Zeeman relaxation rate at ultralow temperatures by as much as 50%. 相似文献
26.
Zdzis?aw Chilmonczyk Jacek Cybulski Agnieszka Szelejewska-Wo?niakowska Andrzej Le? 《Journal of Molecular Structure》1996,385(3):142-207
Conformations of piperazine rings in 8-{4-[4-(2-pyrimidyl)-1-piperazinyl]butyl}-8-azaspiro[4.5]-decane-7,9-dione (buspir-one — 1) and its two analogues 8-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-8-azaspiro[4.5]-decane-7,9-dione (kaspar — 2) and 4,4-dimethyl-1-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-2,6-piperidinedione (mesmar — 3) (Fig. 1) have been studied with the aid of 1H NMR and 13C NMR spectra. For free bases the two bands corresponding to piperazine hydrogen atoms in the spectra broaden considerably with a decrease in temperature to divide into four separate bands, indicating the presence of a dynamic exchange process. A similar dynamic process, but for higher temperatures, was observed for buspirone (1), kaspar (2) and mesmar (3) hydrochlorides. Proton and carbon atom resonance lines have been assigned with the aid of 2D COSY and 2D HETCOR two-dimensional spectra. 相似文献
27.
A novel method to determine of azaarenes in refined and cold‐pressed vegetable oils and animal fats is reported. The method may be used to determine eight most important acridine derivatives (benz[a]acridine, dibenz[a,i]acridine, benz[c]acridine, dibenz[a,j]acridine, 7,9‐dimethylbenz[c]acridine, dibenz[a,h]acridine, dibenz[a,c]acridine, dibenz[c,h]acridine) at a high sensitivity (LOQ in the 2–25 ng kg?1 range), high analyte recovery rates (70.7–98.7%), sufficient linearity within the studied concentration range (r > 0.97). The method is fast, simple, and needs no expensive clean‐up procedures to successfully determine the analytes. Azaarene concentration in the studied oil samples ranged from 2 to 250 ng kg?1. Benz[a]acridine and dibenz[a,j]acridine were the compounds found most commonly and at the highest concentrations. The observed concentrations most probably reflected levels of environmental contamination of raw materials used to produce the analyzed oil/fat samples. 相似文献
28.
29.
Agata Witczak Anna Pohoryło Jacek Cybulski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):711-720
AbstractThe use of organophosphorus pesticides is undeniably beneficial in agriculture and veterinary medicine, but their excessive use can pollute the environment, as well as contaminate foodstuffs. The objective of this study was to assess contamination of vegetables and fruits available in Poland by organophosphate pesticides (ethoprophos, diazinon, chlorpyrifos, chlorpyrifos-methyl, parathion-methyl, fenchlorphos, merfos,, as well as to assess a potential health risk posed to consumers. The pesticide content was determined by gas chromatography-mass spectrometry (GC-MS). The pesticides were detected in the peel and pulp of vegetables and fruits from Polish crops, as well as imported ones. Pesticide levels in most products were higher in the peel than in the pulp. Neither chlorpyrifos-methyl nor fenchlorphos were found in the material under study. Chlorpyrifos was the pesticide occurring in the highest levels in the peel of both vegetables (31?ng?·?g?1 w.w.) and fruit (9.3?ng?·?g?1 w.w.). The Maximum Residue Level (MRL) for parathion-methyl was exceeded in some samples of zucchini pulp of Spanish origin and in the peel of potato from Poland. But levels of other pesticides in the studied vegetables and fruits were significantly lower than the current MRLs. The assessment of consumer health risk showed a significantly lower Lifetime Average Daily Dose (LADD) of pesticides under this study comparing to the Acceptable Daily Intake (ADI). Moreover, the Hazard Quotient (HQ) was low with a maximum of 3.93?×?10?2 for vegetables and 4.26?×?10?3 for fruits. These estimated HQs were within the safe acceptable limits, indicating low risk to human populations from exposure to organophosphorus pesticides in the study area. 相似文献
30.
We analyse the evolution of a two-stage chemical reaction betweentwo neighbouring plumes of reactants. Under the assumption thatthe plumes are approximately Gaussian we derive a system ofordinary differential equations for the total amount, the centroidand the variance of each reactant. We compare the solution ofthese equations with full numerical simulation of the reaction.Excellent agreement is obtained, with solution of the near-Gaussianmodel requiring considerably less computational effort thanthe full simulations. Of key importance is the yield of thereaction, and we discuss this feature in particular. 相似文献