9,328 research outputs found

    Normal edge-colorings of cubic graphs

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    A normal kk-edge-coloring of a cubic graph is an edge-coloring with kk colors having the additional property that when looking at the set of colors assigned to any edge ee and the four edges adjacent it, we have either exactly five distinct colors or exactly three distinct colors. We denote by χN(G)\chi'_{N}(G) the smallest kk, for which GG admits a normal kk-edge-coloring. Normal kk-edge-colorings were introduced by Jaeger in order to study his well-known Petersen Coloring Conjecture. More precisely, it is known that proving χN(G)5\chi'_{N}(G)\leq 5 for every bridgeless cubic graph is equivalent to proving Petersen Coloring Conjecture and then, among others, Cycle Double Cover Conjecture and Berge-Fulkerson Conjecture. Considering the larger class of all simple cubic graphs (not necessarily bridgeless), some interesting questions naturally arise. For instance, there exist simple cubic graphs, not bridgeless, with χN(G)=7\chi'_{N}(G)=7. On the other hand, the known best general upper bound for χN(G)\chi'_{N}(G) was 99. Here, we improve it by proving that χN(G)7\chi'_{N}(G)\leq7 for any simple cubic graph GG, which is best possible. We obtain this result by proving the existence of specific no-where zero Z22\mathbb{Z}_2^2-flows in 44-edge-connected graphs.Comment: 17 pages, 6 figure

    Directed Multicut with linearly ordered terminals

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    Motivated by an application in network security, we investigate the following "linear" case of Directed Mutlicut. Let GG be a directed graph which includes some distinguished vertices t1,,tkt_1, \ldots, t_k. What is the size of the smallest edge cut which eliminates all paths from tit_i to tjt_j for all i<ji < j? We show that this problem is fixed-parameter tractable when parametrized in the cutset size pp via an algorithm running in O(4ppn4)O(4^p p n^4) time.Comment: 12 pages, 1 figur

    Interval matroids and graphs

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    AbstractA base of the cycle space of a binary matroid M on E is said to be convex if its elements can be totally ordered in such a way that for every e ε E the set of elements of the base containing e is an interval. We show that a binary matroid is cographic iff it has a convex base of cycles; equivalently, graphic matroids can be represented as “interval matroids” (matroids associated in a natural way to interval systems). As a consequence, we obtain characterizations of planar graphs and cubic cyclically-4-edge-connected planar graphs in terms of convex bases of cycles

    Proton NMR relaxometry as a useful tool to evaluate swelling processes in peat soils

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    Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H2O molecules by using 1H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1 – T2 and T2 – D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H2O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5 – 50 kJ mol-1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soil

    Nurses\u27 Alumnae Association Bulletin, April 1955

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    Alumnae Notes Annual Giving Committee Reports Digest of Alumnae Meetings Graduation Awards - 1954 Legal Aspects of Nursing Marriages Necrology New Arrivals Physical Advances at Jefferson President\u27s Message School of Nursing Report The Challenge of Neurosurgical Nursin

    Applications of thermal energy storage in the cement industry

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    In the manufacture of cement, literally trillions of Btu's are rejected to the environment each year. The purpose of this feasibility study program was to determine whether thermal energy storage could be used to conserve or allow alternative uses of this rejected energy. This study identifies and quantifies the sources of rejected energy in the cement manufacturing process, established use of this energy, investigates various storage system concepts, and selects energy conservation systems for further study. Thermal performance and economic analyses are performed on candidate storage systems for four typical cement plants representing various methods of manufacturing cement. Through the use of thermal energy storage in conjunction with waste heat electric power generation units, an estimated 2.4 x 10 to the 13th power Btu/year, or an equivalent on investment of the proposed systems are an incentive for further development

    Optoelectronic Reservoir Computing

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    Reservoir computing is a recently introduced, highly efficient bio-inspired approach for processing time dependent data. The basic scheme of reservoir computing consists of a non linear recurrent dynamical system coupled to a single input layer and a single output layer. Within these constraints many implementations are possible. Here we report an opto-electronic implementation of reservoir computing based on a recently proposed architecture consisting of a single non linear node and a delay line. Our implementation is sufficiently fast for real time information processing. We illustrate its performance on tasks of practical importance such as nonlinear channel equalization and speech recognition, and obtain results comparable to state of the art digital implementations.Comment: Contains main paper and two Supplementary Material

    Optimal Dynamical Decoherence Control of a Qubit

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    A theory of dynamical control by modulation for optimal decoherence reduction is developed. It is based on the non-Markovian Euler-Lagrange equation for the energy-constrained field that minimizes the average dephasing rate of a qubit for any given dephasing spectrum.Comment: 6 pages, including 2 figures and an appendi

    The Struggle for Palestinian Hearts and Minds: Violence and Public Opinion in the Second Intifada

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    This paper examines how violence in the Second Intifada influences Palestinian public opinion. Using micro data from a series of opinion polls linked to data on fatalities, we find that Israeli violence against Palestinians leads them to support more radical factions and more radical attitudes towards the conflict. This effect is temporary, however, and vanishes completely within 90 days. We also find some evidence that Palestinian fatalities lead to the polarization of the population and to increased disaffection and a lack of support for any faction. Geographically proximate Palestinian fatalities have a larger effect than those that are distant, while Palestinian fatalities in targeted killings have a smaller effect relative to other fatalities. Although overall Israeli fatalities do not seem to affect Palestinian public opinion, when we divide those fatalities by the different factions claiming responsibility for them, we find some evidence that increased Israeli fatalities are effective in increasing support for the faction that claimed them.Israeli-Palestinian conflict, fatalities, public opinion

    A Model for Granular Texture with Steric Exclusion

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    We propose a new method to characterize the geometrical texture of a granular packing at the particle scale including the steric hindrance effect. This method is based on the assumption of a maximum disorder (entropy) compatible both with strain-induced anisotropy of the contact network and steric exclusions. We show that the predicted statistics for the local configurations is in a fairly agreement with our numerical data.Comment: 9 pages, 5 figure
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