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51.
Olivier Bernardi 《Annals of Combinatorics》2008,12(2):139-153
We give a new characterization of the Tutte polynomial of graphs. Our characterization is formally close (but inequivalent)
to the original definition given by Tutte as the generating function of spanning trees counted according to activities. Tutte’s notion of activity requires a choice of a linear order on the edge set (though the generating function of the activities is, in fact, independent of this order). We define a new
notion of activity, the embedding-activity, which requires a choice of a combinatorial embedding of the graph, that is, a cyclic order of the edges around each vertex. We prove that the Tutte polynomial equals the generating
function of spanning trees counted according to embedding-activities. This generating function is, in fact, independent of the embedding.
Received March 15, 2006 相似文献
52.
J.D. Pedarnig J. Heitz T. Stehrer B. Praher R. Viskup K. Siraj A. Moser A. Vlad M.A. Bodea D. Bäuerle N. Hari Babu D.A. Cardwell 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
Multi-component oxide ceramics and epitaxial oxide thin films are analyzed by laser-induced breakdown spectroscopy (LIBS). Furthermore, pulsed-laser deposition (PLD) of thin films is investigated by long-term monitoring of the optical plasma emission. Both nano-composite high-temperature superconductors (HTS) consisting of YBa2Cu3O7 − δ bulk and Y2Ba4MCuOx (M-2411, M = Ag, Nb) nano-particles, and semiconducting ZnO doped with Aluminum and Lithium are ablated by nano-second laser pulses. The plasma emission is recorded using grating spectrometers with intensified gated detectors. The LIBS signals of nano-particles correlate with the nominal content of the M-2411 phase (0–15 mol%) and reveal a strong signal of Ytterbium impurity (3–35 ppm). In situ monitoring of the PLD process shows element signals that are stable for more than 10,000 laser pulses for both HTS and ZnO ceramics. The relative concentration of elements in thin films and ceramics as determined by LIBS is almost the same. 相似文献
53.
Iain Moffatt 《Journal of Graph Theory》2016,81(4):329-341
In this article we consider minors of ribbon graphs (or, equivalently, cellularly embedded graphs). The theory of minors of ribbon graphs differs from that of graphs in that contracting loops is necessary and doing this can create additional vertices and components. Thus, the ribbon graph minor relation is incompatible with the graph minor relation. We discuss excluded minor characterizations of minor closed families of ribbon graphs. Our main result is an excluded minor characterization of the family of ribbon graphs that represent knot and link diagrams. 相似文献
54.
L. Davidson 《Journal of Turbulence》2016,17(3):274-307
The partially Reynolds-averaged Navier–Stokes (PANS) model can be used to simulate turbulent flows either as RANS, large eddy simulation (LES) or DNS. Its main parameter is fk whose physical meaning is the ratio of the modelled to the total turbulent kinetic energy. In RANS fk = 1, in DNS fk = 0 and in LES fk takes values between 0 and 1. Three different ways of prescribing fk are evaluated for decaying grid turbulence and fully developed channel flow: fk = 0.4, fk = k3/2 tot/? and, from its definition, fk = k/ktot where ktot is the sum of the modelled, k, and resolved, kres, turbulent kinetic energy. It is found that the fk = 0.4 gives the best results. In Girimaji and Wallin, a method was proposed to include the effect of the gradient of fk. This approach is used at RANS– LES interface in the present study. Four different interface models are evaluated in fully developed channel flow and embedded LES of channel flow: in both cases, PANS is used as a zonal model with fk = 1 in the unsteady RANS (URANS) region and fk = 0.4 in the LES region. In fully developed channel flow, the RANS– LES interface is parallel to the wall (horizontal) and in embedded LES, it is parallel to the inlet (vertical). The importance of the location of the horizontal interface in fully developed channel flow is also investigated. It is found that the location – and the choice of the treatment at the interface – may be critical at low Reynolds number or if the interface is placed too close to the wall. The reason is that the modelled turbulent shear stress at the interface is large and hence the relative strength of the resolved turbulence is small. In RANS, the turbulent viscosity – and consequently also the modelled Reynolds shear stress – is only weakly dependent on Reynolds number. It is found in the present work that it also applies in the URANS region. 相似文献
55.
56.
为了开发一种结构简单、控制灵活的冲压自动化装置,文中简述了一种基于Linux下的冲孔自动化生产线,用于薄壁管材的冲孔。设计了以ARM为主控制器,CPLD为协处理器的方式来作为整个生产系统的控制核心。建立了气缸驱动系统和冲压机械手,机械手通过伺服电机的驱动完成取料和旋转,在与冲床的相互配合下完成冲孔要求。构造了生产线系统的故障树,利用定量分析结合定性分析的方式对故障进行分析,采用电容式触摸屏通过界面向操作人员发送故障提示,大大减少了设备停机时间。实验结果表明该系统完全能满足生产要求,稳定可靠,操作便捷,响应速度快。 相似文献
57.
掺杂是调制graphene催化特性的有效方法 .掺杂的石墨烯,因其具有对氧还原反应具有较高的活性,而作为一种新型高效质子交换膜燃料电池阴极材料.采用包含色散力校正的第一性原理的密度泛函理论方法 (DFT-D)系统的研究了O_2在CrN_4掺杂的石墨烯上的吸附和氢化特性.结果表明:(1)O_2倾向于以side-on模式吸附在Cr顶位,形成O-Cr-O三元环结构,吸附能为1.75 e V;(2)O_2在Cr N4-Gra上更倾向于直接分解成O+O,并进一步氢化为O+OH,反应的限速步为O_2的分解,相应的反应势垒为0.48 e V. 相似文献
58.
Suppose G is a graph embedded in Sg with width (also known as edge width) at least 264(2g−1). If P ⊆ V(G) is such that the distance between any two vertices in P is at least 16, then any 5‐coloring of P extends to a 5‐coloring of all of G. We present similar extension theorems for 6‐ and 7‐chromatic toroidal graphs, for 3‐colorable large‐width graphs embedded on Sg with every face even‐sided, and for 4‐colorable large‐width Eulerian triangulations. © 2001 John Wiley & Sons, Inc. J Graph Theory 36: 105–116, 2001 相似文献
59.
Rafal Nowaczynski Marcin Gajc Hancza B. Surma Pawel Osewski Adam Strzep Witold Ryba‐Romanowski Dorota A. Pawlak 《Particle & Particle Systems Characterization》2019,36(1)
Quantum dot (QD)‐based light‐emitting materials are gaining increased attention because of their easily tunable optical properties desired for various applications in biology, optoelectronics, and photonics. However, few methods can be used to manufacture volumetric materials doped with more than one type of QD other than QD‐polymer hybrids, and they often require complicated preparation processes and are prone to luminescence quenching by QD aggregation and separation from the matrix. Here, simultaneous doping of a volumetric glass‐based nanocomposite with two types of QDs is demonstrated for the first time in a single‐step process using the nanoparticle direct doping method. Glass rods doped with CdTe, CdSe/ZnS, or co‐doped with both QDs, are obtained. Photoluminescence and lifetime experiments confirm temperature‐dependent double emission with maxima at 596 and 720 nm with mean lifetimes up to 16 ns, as well as radiative energy transfer from the short wavelength–emitting QDs to the long wavelength–emitting QDs. This approach may enable the simple and cost‐efficient manufacturing of bulk materials that produce multicolor luminescence with cascade excitation pumping. Applications that could benefit from this include broadband optical fiber amplifiers, backlight systems in LCD screens, high‐power LEDs, or down‐converting solar concentrators used to increase the efficiency of solar panels. 相似文献
60.