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51.
Roger F. Bartholomew 《Journal of Non》1973,12(3):321-332
The electrical properties of glasses in the Na2OP2O5, Ag2OP2O5 and (1?x)Na2OxAg2OP2O5 systems have been measured over a range of temperature and composition.The properties of the Na2OP2O5 and Ag2OP2O5 glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na2O?xAg2O?P2O5 system was found around the mole ratio of 0.16:0.84 Ag2O:Na2O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the Tg-against-composition plots. A linear relationship was noted for the tan δ-versus-log10 (resistivity) plot, as has been seen in other glass-forming systems. 相似文献
52.
CH. Sedlmair K. Seshan A. Jentys J. A. Lercher 《Research on Chemical Intermediates》2003,29(3):257-269
The influence of SO2 exposure under lean (oxidizing) and rich (reducing) reaction conditions on the storage and oxidation/reduction function of a commercial NOx storage-reduction catalyst was investigated by temperature-programmed uptake experiments and high temperature XRD. Both the storage capacity and the oxidation/reduction function of the catalyst were deactivated by SO2 exposure under lean and rich reaction conditions. The deactivation of the storage component, i.e. the loss of the NOx storage capacity, resulted mainly from the formation of Ba-sulfates accumulating in the bulk phase, which have a high thermal stability (>800°C) and, therefore, cannot be removed under the typical operation conditions of a NSR catalyst. For the oxidation function only a temporarily deactivation during lean reaction conditions was observed. Besides the formation of SO2-
4 species on the storage component at the beginning of the SO2 exposure under rich conditions, an adsorption of SO2 on the noble metal component was observed resulting in the formation of sulfur deposits. The oxidation of these sulfur species with a subsequent spillover of SO2-
4 species to the storage component during lean conditions could accelerate the deactivation of the storage capacity. 相似文献
53.
Caroline Yoon Barbara Kensington-Miller Jamie Sneddon Hannah Bartholomew 《International Journal of Mathematical Education in Science & Technology》2013,44(8):1107-1122
Students often play a passive role in large-scale lectures in undergraduate mathematics courses: they observe the lecturer demonstrate mathematical procedures, but they rarely engage in authentic mathematical activity themselves. This study uses semi-structured interviews of undergraduate students to investigate the implicit and explicit social norms and expectations that influence students to maintain their passive roles during lectures. Students were aware that their passivity was influenced by social norms, but perceived these norms as necessary for allowing the lecturer to get through the content in the allotted lecture time, while enabling students to avoid being publicly embarrassed in the lecture. However, the students appreciated opportunities to work on examples in small groups during lectures. We argue that the success of small group interactions during large-scale lectures depends on students and lecturers establishing supportive social norms, and adjusting their lecture goals from ‘covering the content’ to ‘developing mathematical understanding’. 相似文献
54.
O. Petracic S. Sahoo CH. Binek W. Kleemann J.B. Sousa S. Cardoso 《Phase Transitions》2013,86(4-5):367-375
Ac susceptibility measurements were performed on discontinuous magnetic multilayers [Co 80 Fe 20 ( t )/Al 2 O 3 (3 nm)] 10 , t = 0.9 and 1.0 nm, by Superconducting Quantum Interference Device (SQUID) magnetometry. The CoFe forms nearly spherical ferromagnetic single-domain nanoparticles in the diamagnetic Al 2 O 3 matrix. Due to dipolar interactions and random distribution of anisotropy axes the system exhibits a spin-glass phase. We measured the ac susceptibility as a function of temperature 20 h T h 100 K at different dc fields and as a function of frequency 0.01 h f h 1000 Hz. The spectral data were successfully analyzed by use of the phenomenological Cole-Cole model, giving a power-law temperature dependence of the characteristic relaxation time c and a high value for the polydispersivity exponent, f , 0.8, typical of spin glass systems. 相似文献
55.
Tai V. Truong Aaron N. Nackos Jacolin A. Murray Jon A. Kimball Jason E. Hawkes Donald J. Harvey H. Dennis Tolley Richard A. Robison Calvin H. Bartholomew Milton L. Lee 《Journal of chromatography. A》2009,1216(40):6852-6857
A simple device for field sampling and concentration of analytes for subsequent introduction into an injection port for gas chromatographic (GC) analysis has been developed. It consists of a tiny, coiled platinum wire filament (CWF) that is attached to a retractable plunger wire, which fits inside a syringe needle housing. Sampling is accomplished by dipping the end of the CWF in a liquid sample, which is drawn into the wire coil by capillary action, and introducing it into the injection port either before or after allowing the solvent to evaporate. The CWF can be used with or without a nonvolatile chemical coating. A major advantage of this sampling device is that nonvolatile sample matrix components remain on the wire coil, reducing the required injection port and liner cleaning frequency and contamination of the head of the chromatographic column. The coil itself can be easily cleaned between analyses by rinsing and/or burning off residual material in a small flame. The sampling coil facilitates specifically designed chemical reactions in the injection port, such as thermochemolysis and methylation. Applications demonstrated in this work include: (1) direct introduction of samples with little or no pre-treatment, (2) simultaneous thermochemolysis and methylation of lipid-containing samples such as bacteria and bacterial endospores for analysis of biomarkers, and (3) solid phase micro-extraction (SPME) using temporary wire coatings. The CWF allowed for significant reduction in sample preparation time, in most cases to less than a few minutes. The peak shapes examined for polycyclic aromatic hydrocarbon analytes (PAHs) were significantly better (asymmetry factors <1.3) when using the CWF sampling technique compared to splitless and on-column injection techniques (asymmetry factors >1.3). Extraction efficiencies for SPME (especially for high boiling point components such as PAHs) improved by an average of 2.5 times when using the CWF compared to the performance of commercially available SPME fibers. Coiled wire filaments and GC injection port liners were used for more than 100 Bacillus endospore thermochemolysis methylation analyses without the need for cleaning or replacement. 相似文献
56.
Amymarie K. Bartholomew Cristin E. Juda Jonathon N. Nessralla Benjamin Lin SuYin Grass Wang Yu‐Sheng Chen Theodore A. Betley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5743-5747
The trichromium cluster (tbsL)Cr3(thf) ([tbsL]6?=[1,3,5‐C6H9(NC6H4‐o‐NSitBuMe2)3]6?) exhibits steric‐ and solvation‐controlled reactivity with organic azides to form three distinct products: reaction of (tbsL)Cr3(thf) with benzyl azide forms a symmetrized bridging imido complex (tbsL)Cr3(μ3‐NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex (tbsL)Cr3(μ1‐NMes); whereas the reaction with mesityl azide in THF leads to terminal N‐atom excision from the azide to yield the nitride complex (tbsL)Cr3(μ3‐N). The reactivity of this complex demonstrates the ability of the cluster‐templating ligand to produce a well‐defined polynuclear transition metal cluster that can access distinct single‐site and cooperative reactivity controlled by either substrate steric demands or reaction media. 相似文献
57.
M. Djebara M. Asghar J.P. Bocquet R. Brissot M. Maurel H. Nifenecker CH. Ristori 《Nuclear Physics A》1984,425(1):120-140
A gas ΔE ? ER telescope has been used to measure charge yields and their correlations with kinetic energies for 229Th and 232U. Even-charge yields are enhanced compared with odd-charge yields for both fissioning systems; this enhancement increases for events with higher kinetic energy. The mean odd-even effect ; it is . The energy-integrated δp and δp for different energy windows, vary strongly as a function of charge (Z) due to the underlying shells. The δp averaged over Z increases fast with kinetic energy, contrary to the existing results for 233U and 235U, where δp flattens off at low energies. For both systems, the most probable kinetic energy ē shows a strong odd-even stagger; the mean odd-even effect on energy, the latter is about twice the value for . These results are discussed in terms of the existing models. 相似文献
58.
The acid catalysed rearrangement of an acetal derived from 2-hydroxymethyl-3-butene-l-ol proceeding via an intramolecular cation-olefin cyclisation provides access to a 4-hydroxytetrahydropyran and thence to (±)-talaromycin B. 相似文献
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