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91.
David L. Powers 《Journal of Graph Theory》1982,6(1):43-55
If n is divisible by at least three distinct primes, the dihedral group Dn can be generated by three nonredundant, involuntary elements. We study the Cayley graphs resulting from such a presentation of Dn for several families of n and for all admissible n < 120. All these graphs are trivalent, bipartite, Hamiltonian, of girth 6, and are regular representations of their groups. For each n, the isomorphism classes are determined and the graphs are described by a simple code. 相似文献
92.
K. E. Lu G. S. Glaesemann M. T. Lee D. R. Powers J. S. Abbott 《Optical and Quantum Electronics》1990,22(3):227-237
Corning's hermetically coated fibre has been evaluated for mechanical and hydrogen performance under severe test conditions using large sample sizes. The results indicate that the carbon coating is truly hermetic, and that it provides an effective barrier for preventing hydrogen and water from reaching the glass surface. As a result the hermetically coated fibre possesses superior resistance to fatigue and hydrogen permeation over standard fibre. These attributes make this hermetically coated fibre and excellent candidate for use in terrestrial communication and undersea cables, as well as in other special applications where a harsh environment is present. 相似文献
93.
Richard S Stein Joseph Powers 《高分子科学》2005,23(5):i0006-i0006
This important book emphasizes the basic derivation of many key equations used in polymer physics. Phrases such as “it can be easily shown that” and “it readily follows that”, seen in many textbooks, are seldom used here. The models, assumptions and key equations underlying concepts are presented in the text; details used in the derivations are given in the accompanying CD-Rom. The CD-Rom also contains problems (with solutions in many cases) which test the reader's grasp of the material, as well as a glossary of symbols. 相似文献
94.
95.
Let L be a lattice of finite length, ξ = (x 1,…, x k )∈L k , and y ∈ L. The remoteness r(y, ξ) of y from ξ is d(y, x 1)+?+d(y, x k ), where d stands for the minimum path length distance in the covering graph of L. Assume, in addition, that L is a graded planar lattice. We prove that whenever r(y, ξ) ≤ r(z, ξ) for all z ∈ L, then y ≤ x 1∨?∨x k . In other words, L satisfies the so-called c 1 -median property. 相似文献
96.
Powers DC Leber PA Gallagher SS Higgs AT McCullough LA Baldwin JE 《The Journal of organic chemistry》2007,72(1):187-194
At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate. 相似文献
97.
Koev ST Powers MA Yi H Wu LQ Bentley WE Rubloff GW Payne GF Ghodssi R 《Lab on a chip》2007,7(1):103-111
While microcantilevers offer exciting opportunities for mechano-detection, they often suffer from limitations in either sensitivity or selectivity. To address these limitations, we electrodeposited a chitosan film onto a cantilever surface and mechano-transduced detection events through the chitosan network. Our first demonstration was the detection of nucleic acid hybridization. In this instance, we electrodeposited the chitosan film onto the cantilever, biofunctionalized the film with oligonucleotide probe, and detected target DNA hybridization by cantilever bending in solution (static mode) or resonant frequency shifts in air (dynamic mode). In both detection modes, we observed a two-order of magnitude increase in sensitivity compared to values reported in literature for DNA immobilized on self-assembled monolayers. In our second demonstration, we coupled electrochemical and mechanical modes to selectively detect the neurotransmitter dopamine. A chitosan-coated cantilever was biased to electrochemically oxidize dopamine solution. Dopamine's oxidation products react with the chitosan film and create a tensile stress of approximately 1.7 MPa, causing substantial cantilever bending. A control experiment was performed with ascorbic acid solution. It was shown that the electrochemical oxidation of ascorbic acid does not lead to reactions with chitosan and does not change cantilever bending. These results suggest that chitosan can confer increased sensitivity and selectivity to microcantilever sensors. 相似文献
98.
Amir Golmohamadi Gregory Möller Joseph Powers Caleb Nindo 《Ultrasonics sonochemistry》2013,20(5):1316-1323
Ultrasound in the 20–1000 kHz range show unique propagation characteristics in fluid media and possess energy that can break down fruit matrices to facilitate the extraction of valuable bioactive compounds. Red raspberries carry significant amounts of specific antioxidants, including ellagitannins and anthocyanins that are important for human health. The objective of this study was to investigate the effects of ultrasound frequencies associated with cavitation (20 kHz) and microstreaming (490 and 986 kHz) on total antioxidant activity (AOA), total phenolics content (TPC), and total monomeric anthocyanin content (ACY) of red raspberry puree prepared from crushed berries. The pureed fruit was subjected to high-intensity (20 kHz) and higher frequency-low intensity (490 and 986 kHz) ultrasound for 30 min. The temperature of treated purees increased to a maximum of 56 °C with 986 kHz. Sonication at 20 and 490 kHz significantly (p < 0.05) affected the AOA, ACY, and TPC of red raspberry puree, while 986 kHz had no significant effect on ACY and AOA (p < 0.05). In all cases, ultrasound treatment had significant and positive effect on at least one of the measured parameters up to 30 min. Sonication beyond 10 min (and up to 30 min) using 20 kHz either produced no change or caused a drop in AOA and ACY. However, for 986 and 20 kHz, TPC, increased by 10% and 9.5%, respectively after 30 min (p < 0.05) compared to the control. At 20 kHz, AOA and ACY increased by 17.3% and 12.6% after 10 min. It was demonstrated that 20 kHz ultrasound treatment, when limited to 10 min, was the most effective for extraction of bioactive compounds in red raspberry compared to 490 and 986 kHz although the effect could be similar at the higher frequencies if different amplitudes are used. 相似文献
99.
Solfrizzo M Gambacorta L Lattanzio VM Powers S Visconti A 《Analytical and bioanalytical chemistry》2011,401(9):2831-2841
Humans and animals can be simultaneously exposed through the diet to different mycotoxins, including aflatoxins, ochratoxin
A, deoxynivalenol, zearalenone, and fumonisins, which are the most important. Evaluation of the frequency and levels of human
and animal exposure to these mycotoxins can be performed by measuring the levels of the relevant biomarkers in urine. Available
data on the toxicokinetics of these mycotoxins in animals suggest that aflatoxin M1 (AFM1), ochratoxin A (OTA), deoxynivalenol (DON)/de-epoxydeoxynivalenol (DOM-1), alpha-zearalenol (α-ZOL)/beta-zearalenol (β-ZOL),
and fumonisin B1 (FB1) can be used as urinary biomarkers. A liquid chromatographic–tandem mass spectrometric method has been developed for simultaneous
determination of these mycotoxin biomarkers in human or animal urine. Urine samples were purified and concentrated by a double
cleanup approach, using a multitoxin immunoaffinity column and a reversed-phase SPE Oasis HLB column. Separation of the biomarkers
was performed by reversed-phase chromatography using a multi-step linear methanol–water gradient containing 0.5% acetic acid
as mobile phase. Detection and quantification of the biomarkers were performed by triple quadrupole mass spectrometry (LC–ESI-MS/MS).
The clean-up conditions were optimised to obtain maximum analyte recovery and high sensitivity. Recovery from spiked samples
was performed at four levels in the range 0.03–12 ng mL−1, using matrix-matched calibration curves for quantification. Mean recoveries of the biomarkers tested ranged from 62 to 96%
with relative standard deviations of 3–20%. Enzymatic digestion with β-glucuronidase/sulfatase resulted in increased concentrations
of the biomarkers, in both human and pig urine, in most samples containing measurable concentrations of DON, DOM-1, OTA, α-ZOL,
or β-ZOL. A highly variable increase was observed between individuals. Co-occurrence of OTA and DON in human urine is reported
herein for the first time. 相似文献
100.
Kuppuswamy S Cooper BG Bezpalko MW Foxman BM Powers TM Thomas CM 《Inorganic chemistry》2012,51(3):1866-1873
The heterobimetallic complexes [Mn((i)PrNPPh(2))(3)Cu((i)PrNHPPh(2))] (1) and [Fe((i)PrNPPh(2))(3)Cu((i)PrNHPPh(2))] (2) have been synthesized by the one pot reaction of LiN(i)PrPPh(2), MCl(2) (M = Mn, Fe), and CuI in high yield. Addition of excess CuI into 2 or directly to the reaction mixture led to the formation of a heterotrimetallic [Fe((i)PrNPPh(2))(3)Cu(2)((i)PrNPPh(2))] (3) in good yield. Complexes 1-3 have been characterized by means of elemental analysis, paramagnetic (1)H NMR, UV-vis spectroscopy, cyclic voltammetry, and single crystal X-ray analysis. In all three complexes, Mn or Fe are in the +2 oxidation state and have a high spin electron configuration, as evidenced by solution Evans' method. In addition, the oxidation state of Fe in complex 3 is confirmed by zero-field (57)Fe M?ssbauer spectroscopy. X-ray crystallography reveals that the three coordinate Mn/Fe centers in the zwitterionic complexes 1-3 adopt an unusual trigonal planar geometry. 相似文献