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91.
A. E. Brouwer 《Aequationes Mathematicae》1982,25(1):77-82
We investigate the polarities of G. Higman's symmetric 2-(176, 50, 14) design and find that there are two of them (up to conjugacy), one having 80 and the other 176 absolute points. From the latter we can derive a strongly regular graph with parameters (v, k, , )=(176, 49, 12, 14). Its group of automorphisms is Sym(8) with orbits of size 8 and 168 on the vertices. It does not carry a partial geometry or a delta space, and is not the result of mergingd=1 andd=2 in a distance regular graph with diameter 3 and girth 6 on 176 vertices. 相似文献
92.
Eric Hughes Eric B. Brouwer Robin K. Harris 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,138(2):256
For compounds giving “crowded” 1-dimensional magic-angle-spinning spectra, information about the local atomic environment in the form of the chemical shift anisotropy (CSA) is sacrificed for high resolution of the less informative isotropic chemical shift. Magic-angle-turning (MAT) NMR pulse sequences preserve the CSA information by correlating it to the isotropic chemical shift in a 2-dimensional experiment. For low natural abundance nuclei such as 13C and 15N and under 1H heteronuclear dipolar decoupling conditions, the dominant NMR interaction is the chemical shift. For abundant nuclei such as 1H, 19F, and 31P, the homonuclear dipolar interaction becomes a significant contribution to the observed linewidth in both F1 and F2 dimensions. We incorporate MREV8 homonuclear multiple-pulse decoupling sequences into the MAT experiment to give a multiple-pulse MAT (MP-MAT) experiment in which the homonuclear dipolar interaction is suppressed while maintaining the chemical shift information. Extensive use of computer simulation using GAMMA has guided the pulse sequence development. In particular, we show how the MREV8 pulses can be incorporated into a quadrature-detected sequence such as MAT. The MP-MAT technique is demonstrated for a model two-site system containing a mixture of silver trifluoroacetate and calcium difluoride. The resolution in the isotropic evolution dimension is improved by faster sample spinning, shorter MREV8 cycle times in the evolution dimension, and modifications of the MAT component of the pulse sequence. 相似文献
93.
Brouwer N Liu Q Harrington D Kohen J Vemulpad S Jamie J Randall M Randall D 《Molecules (Basel, Switzerland)》2005,10(10):1252-1262
The Australian Aboriginal people have used plants as medicine and food for thousands of years, however, this traditional knowledge is documented only to a limited extent, and is in danger of being lost. The Indigenous Bioresources Research Group (IBRG) aims to help Australian Aboriginal communities to preserve their customary medicinal knowledge, and to provide information that can be used for their cultural or educational purposes, as well as for scientific advancement. This work is undertaken in close collaboration with Australian Aboriginal communities in New South Wales. The project is multidisciplinary, combining an ethnobotanical and an ethnopharmacological approach, which includes biological and chemical investigations, as well as developing best practices for protecting traditional knowledge. This paper describes the general strategy of the project as well as methods used in the ethnopharmacological study. Ethnobotanical databases are set up for each participating community. Plant material is collected, extracted, and active compounds are isolated using a bioassay-guided fractionation approach. All extracts and compounds are tested for biological activity in antimicrobial assays (disc diffusion, resazurin, fluorescein diacetate), neurological assays or anti-inflammatory assays, depending on their traditional use. 相似文献
94.
L. E. J. Brouwer 《Mathematische Annalen》1911,71(3):320-327
Ohne Zusammenfassung 相似文献
95.
We show fort>3 the nonexistence of binary [2
t
–2, 2
t
–2t–1, 5] codes. 相似文献
96.
We construct vertex-transitive graphs Γ, regular of valency k=n2+n+1 on
vertices, with integral spectrum, possessing a distinguished complete matching such that contracting the edges of this matching yields the Johnson graph J(2n, n) (of valency n2). These graphs are uniformly geodetic in the sense of Cook and Pryce (1983) (F-geodetic in the sense of Ceccharini and Sappa (1986)), i.e., the number of geodesics between any two vertices only depends on their distance (and equals 4 when this distance is two). They are counterexamples to Theorem 3.15.1 of [1], and we show that there are no other counterexamples. 相似文献
97.
Aart Blokhuis Andries E. Brouwer Willem H. Haemers 《Designs, Codes and Cryptography》2007,44(1-3):293-305
We give some necessary conditions for a graph to be 3-chromatic in terms of the spectrum of the adjacency matrix. For all known distance-regular graphs it is determined whether they are 3-chromatic. A start is made with the classification of 3-chromatic distance-regular graphs, and it is shown that such graphs, if not complete 3-partite, must have λ ≤ 1. 相似文献
98.
We construct a bipartite distance-regular graph with intersection array {45, 44, 36, 5; 1, 9, 40, 45} and automorphism group 35 :(2 ×M10) (acting edge-transitively) and discuss its relation to previously known combinatorial structures. 相似文献
99.
A method, based on Tits' work and involving an idea of M. Ronan, is developed in order to recognize certain geometries which are locally buildings of classical type as quotients of buildings. Two applications are treated in detail showing that every finite nearly classical near polygon must be a dual polar space and that in the finite case of Cooperstein's theorem characterizing geometries of Lie type D
n
, the hypotheses can be weakened considerably. 相似文献
100.
Tiina?J.?Kauppila Andries?P.?BruinsEmail author Risto?Kostiainen 《Journal of the American Society for Mass Spectrometry》2005,16(8):1399-1407
In the novel atmospheric pressure photoionization-mass spectrometry the ionization efficiency has been observed to decrease
when the solvent flow rate is increased. The effect of the flow rate on the ionization efficiency was studied by comparing
the behavior of two analytes, one of which is ionized through charge exchange, the other through proton transfer. Additional
information about the ion loss mechanisms was obtained by comparing results obtained with two different APPI ion sources:
a Sciex prototype and the Agilent/Syagen APPI source. In addition to the measurements done by using the mass analyzer, the
total ion current in the ion source was obtained by measuring the currents of the ions arriving at curtain/end plate and orifice/capillary
of the two mass spectrometers. The total ion current measurements showed a significant decrease at high solvent flow rates.
Loss of dopant radical cations was thought to be the reason for the signal decrease of the analytes formed through charge
exchange. Analytes formed through proton transfer were not as seriously ected by the high solvent flow rates, but some saturation
of their signal was nevertheless observed. Loss of photons through absorption by solvent vapor is another mechanism that can
be held responsible for a reduction of the total number of ions produced by the APPI source. 相似文献