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251.
252.
John Conway John McKay Abdellah Sebbar 《Proceedings of the American Mathematical Society》2004,132(8):2233-2240
We characterize the 171 discrete subgroups of occurring in Monstrous Moonshine in terms of their group-theoretic properties alone.
253.
We report the results of experiments to estimate the moisture expansion of several modern and ancient clay brick ceramics from the time of manufacture. From these data we propose a new expansion law, in which the expansive strain increases as (age)(1/4) approximately. Such time dependence is consistent with a mechanism in which expansion arises from a diffusion-controlled rehydration reaction on a linear or low-dimension structure. Our results provide new guidance for the engineering design of masonry and suggest a possible new method for archaeological dating of ceramics. 相似文献
254.
A new ultrasonic method — thermoacoustic analysis — is reported for the detection of the added chemical preservatives in branded
milk. The nature of variation and shift in the thermal response of the acoustic parameters specific acoustic impedance, adiabatic
compressibility and Rao’s specific sound velocity for different samples of branded milk as compared to the chemical added
pure milk are explained as due to the presence of chemicals in these branded samples. 相似文献
255.
The edit distance between two graphs on the same vertex set is defined to be the size of the symmetric difference of their edge sets. The edit distance function of a hereditary property, , is a function of p, and measures, asymptotically, the furthest graph of edge density p from under this metric. In this article, we address the hereditary property , the property of having no induced copy of the complete bipartite graph with two vertices in one class and t in the other. Employing an assortment of techniques and colored regularity graph constructions, we are able to determine the edit distance function over the entire domain when and extend the interval over which the edit distance function for is known for all values of t, determining its maximum value for all odd t. We also prove that the function for odd t has a nontrivial interval on which it achieves its maximum. These are the only known principal hereditary properties for which this occurs. In the process of studying this class of functions, we encounter some surprising connections to extremal graph theory problems, such as strongly regular graphs and the problem of Zarankiewicz. 相似文献
256.
Esa A. Jaatinen Matthew P. Adams Alison Chou Nick McKay Parry Peter M. Fredericks 《Journal of Raman spectroscopy : JRS》2014,45(8):636-641
The surface enhanced Raman scattering effect has shown immense potential for detecting trace amounts of explosive vapor molecules. To date, efforts to produce a commercially available, reliable SERS sensor have been impeded by an inability to separate the electromagnetic enhancement produced by the metallic nanostructure from other signal enhancing effects. Here, we show a new Raman sensor that uses surface acoustic waves (SAWs) to produce controllable surface structures on gold films deposited on LiNbO3 substrates that modulate the Raman signal of a target compound (thiophenol) adsorbed on the films. We demonstrate that this sensor can dynamically control the Raman signal simply by changing the SAW's amplitude, allowing the Raman signal enhancement factor to be directly measured with no variation in the concentration of the target compound. The physically adsorbed molecules can be removed from the sensor without physical cleaning or damage, making it possible to reuse it for real‐time Raman detection. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
257.
McKay CS Blake JA Cheng J Danielson DC Pezacki JP 《Chemical communications (Cambridge, England)》2011,47(36):10040-10042
Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes proceed with rate constants up to 3.38 ± 0.31 M(-1) s(-1) in CD(3)CN, or 59 times faster than the analogous reaction of azides. This highly specific modular labeling strategy can be applied for direct labeling of proteins and for live cell imaging of cancer cells. 相似文献
258.
259.
Richard E. Russo Alexander A. Bol'shakov Xianglei Mao Christopher P. McKay Dale L. Perry Osman Sorkhabi 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(2):99-104
A new method of performing optical isotopic analysis of condensed samples in ambient air and at ambient pressure has been developed: Laser Ablation Molecular Isotopic Spectrometry (LAMIS). The technique uses radiative transitions from molecular species either directly vaporized from a sample or formed by associative mechanisms of atoms or ions in a laser ablation plume. This method is an advanced modification of a known atomic emission technique called laser-induced breakdown spectroscopy (LIBS). The new method — LAMIS — can determine not only chemical composition but also isotopic ratios of elements in the sample. Isotopic measurements are enabled by significantly larger isotopic shifts found in molecular spectra relative to atomic spectra. Analysis can be performed from a distance and in real time. No sample preparation or pre-treatment is required. Detection of the isotopes of hydrogen, boron, carbon, and oxygen are discussed to illustrate the technique. 相似文献
260.
Stevens CJ Dallanegra R Chaplin AB Weller AS Macgregor SA Ward B McKay D Alcaraz G Sabo-Etienne S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(10):3011-3020
The IrIII fragment {Ir(PCy3)2(H)2}+ has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H3B?NMe2H ( A ) to ultimately give dimeric aminoborane [H2BNMe2]2 ( D ). Addition of A to [Ir(PCy3)2(H)2(H2)2][BArF4] ( 1 ; ArF=(C6H3(CF3)2), gives the amine‐borane complex [Ir(PCy3)2(H)2(H3B?NMe2H)][BArF4] ( 2 a ), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy3)2(H)2(H2B? NMe2)][BArF4] ( 3 ). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H2 loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3 . DFT calculations indicate that this involves metal trapping of the monomer–dimer equilibrium, 2 H2BNMe2 ? [H2BNMe2]2. Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy3)2(H)2(NCMe)2][BArF4] ( 6 ) liberating H2B? NMe2 ( B ), which then dimerises to give D . This is shown to be a second‐order process. It also allows on‐ and off‐metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine‐borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H3B?NMe2BH2?NMe2H ( C ), which ultimately was converted to D . These results indicate that the metal is involved in both the dehydrogenation of A , to give B , and the oligomerisation reaction to afford C . A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D , with 3 observed as the final organometallic product, suggesting a B? N bond cleavage mechanism. Complex 6 does not react with C , but in combination with B oligomer C is consumed to eventually give D , suggesting an additional role for free aminoborane in the formation of D from C . 相似文献