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171.
The orientational ordering of several liquid crystals containing a difluorosubstituted phenyl ring has been studied through the use of C-13 NMR. The fluorinated phenyl ring of these liquid crystals have Cs symmetry, so three order parameters are required to completely describe the ordering of this ring. All three of these order parameters have been calculated from carbon-fluorine dipolar coupling constants obtained from the carbon-fluorine splittings in the C-13 NMR spectra. Because of the complexity of the fluorine-coupled spectra, variable angle spinning (VAS) was used to resolve the carbon-fluorine splittings. In order to study the orientational ordering over wide ranges of temperature, we have developed an empirical correlation between the order parameter and the value of a carbon-fluorine dipolar coupling constant. This enabled us to study the change in the order parameter with temperature. The results of applying this method to several structurally similar liquid crystals containing the same type of difluorinated phenyl ring are presented. A comparison is made to a similar mono-fluorinated liquid crystal. 相似文献
172.
A review of otoacoustic emissions 总被引:32,自引:0,他引:32
R Probst B L Lonsbury-Martin G K Martin 《The Journal of the Acoustical Society of America》1991,89(5):2027-2067
Otoacoustic emissions measured in the external ear canal describe responses that the cochlea generates in the form of acoustic energy. For the convenience of discussing their principal features, emitted responses can be classified into several categories according to the type of stimulation used to evoke them. On this basis, four distinct but interrelated classes can be distinguished including spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. The present review details the findings that have been described for each emission type according to this classification schema. Additionally, the known features of emitted responses are discussed for both normally hearing and hearing-impaired humans and experimental animals, and with respect to their potential clinical applications. The findings reviewed here clearly indicate that future studies of otoacoustic emissions will significantly increase our understanding of the basic mechanisms of cochlear function while, at the same time, provide a new and important clinical tool. 相似文献
173.
Dragan DJURCIC Aleksandar TORGASEV 《数学学报(英文版)》2006,22(3):689-692
In this paper, we prove some properties of the Seneta sequences and functions, and in particular we prove a representation theorem in the Karamata sense for the sequences from the Seneta class SOc. 相似文献
174.
V.A. Khoze A.D. Martin M.G. Ryskin 《The European Physical Journal C - Particles and Fields》2002,24(3):459-468
The rich structure of photon-exchange processes at hadron colliders is studied. We discuss central vector meson production
, W production and production. Each process has distinct, and large, soft pp rescattering effects, which can be directly observed by detecting the outgoing protons. This allows a probe of the optical
density of the proton, which plays a crucial role in the evaluation of the rapidity gap survival probabilities in diffractive-like
processes at hadron colliders. We note that an alternative mechanism for production is odderon, instead of photon, exchange; and that the ratio of odderon to photon contributions is enhanced (suppressed)
for vector meson production.
Received: 1 February 2002 / Revised version: 4 April 2002 / Published online: 22 May 2002 相似文献
175.
Crystals of (Rb0.1(NH4)0.9)2SO4 solid solutions are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameter a exhibits an anomalous behavior, namely, the “invar effect” at temperatures above the ferroelectric phase transition point T c and an anomalous increase in the temperature range from T c to the liquid-helium temperature. An anomalous increase in the lattice parameter a and an increase in the intensity of Bragg reflections with a decrease in the temperature are interpreted within the model of the coexistence of two sublattices hypothetically responsible for the ferroelectric phase transition. A series of superstructure reflections observed along the basis axes corresponds to a sublattice formed in the matrix of the host structure. Analysis of the ratio between the lattice parameters of these structures allows the inference that, in the temperature range 4.2–300 K, the structure of the crystal under investigation can be considered an incommensurate single-crystal composite. 相似文献
176.
Marston Conder Aleksander Malnič Dragan Marušič Primž Potočnik 《Journal of Algebraic Combinatorics》2006,23(3):255-294
A list is given of all semisymmetric (edge- but not vertex-transitive) connected finite cubic graphs of order up to 768. This
list was determined by the authors using Goldschmidt's classification of finite primitive amalgams of index (3,3), and a computer
algorithm for finding all normal subgroups of up to a given index in a finitely-presented group. The list includes several
previously undiscovered graphs. For each graph in the list, a significant amount of information is provided, including its
girth and diameter, the order of its automorphism group, the order and structure of a minimal edge-transitive group of automorphisms,
its Goldschmidt type, stabiliser partitions, and other details about its quotients and covers. A summary of all known infinite
families of semisymmetric cubic graphs is also given, together with explicit rules for their construction, and members of
the list are identified with these. The special case of those graphs having K1,3 as a normal quotient is investigated in detail.
Supported in part by N.Z. Marsden Fund (grant no. UOA 124) and N.Z. Centres of Research Excellence Fund (grant no. UOA 201)
Supported in part by “Ministrstvo za šolstvo, znanost in šport Slovenije”, research program no. 101-506.
Supported in part by research projects no. Z1-4186-0101 and no. Z1-3124-0101. The fourth author would like to thank the University
of Auckland for hospitality during his visit there in 2003. 相似文献
177.
Gašper Jaklič Jernej Kozak Marjeta Krajnc Vito Vitrih Emil Žagar 《Numerical Algorithms》2007,45(1-4):49-60
In this paper, three-pencil lattices on triangulations are studied. The explicit representation of a lattice, based upon barycentric
coordinates, enables us to construct lattice points in a simple and numerically stable way. Further, this representation carries
over to triangulations in a natural way. The construction is based upon group action of S
3 on triangle vertices, and it is shown that the number of degrees of freedom is equal to the number of vertices of the triangulation.
相似文献
178.
A. I. Khil’ko A. G. Luchinin V. G. Burdukovskaya I. P. Smirnov 《Acoustical Physics》2007,53(3):381-392
Potentialities of observing spatially localized inhomogeneities by the low-frequency low-mode pulsed diffraction tomography in a shallow sea are analyzed. A numerically simulated model is used to study the procedure of reconstructing the parameters of inhomogeneities by coprocessing the signals of the tomographic projections formed at the multistatic excitation and reception of low-frequency low-mode acoustic pulses. 相似文献
179.
Martin Loeser Lorenzo Occhi Christian Vélez Raffaele Rezzonico Bernd Witzigmann 《Optical and Quantum Electronics》2006,38(12-14):1069-1075
The impact of self-heating and cavity length on the spectral emission properties of SLEDs is investigated using a state-of-the-art simulation tool. Simulated data are compared to measurements for two InP-based benchmark devices operating around 1300 nm, and excellent agreement is achieved in either case. 相似文献
180.
Motivated by Gauss's first proof of the Fundamental Theorem of Algebra, we study the topology of harmonic algebraic curves.
By the maximum principle, a harmonic curve has no bounded components; its topology is determined by the combinatorial data
of a noncrossing matching. Similarly, every complex polynomial gives rise to a related combinatorial object that we call a
basketball, consisting of a pair of noncrossing matchings satisfying one additional constraint. We prove that every noncrossing
matching arises from some harmonic curve, and deduce from this that every basketball arises from some polynomial. 相似文献