184 research outputs found

    Recent results on well-balanced orientations

    Get PDF
    In this paper we consider problems related to Nash-Williams´ Strong Orientation Theorem and Odd-Vertex Pairing Theorem. These theorems date to 1960 and up to now not much is known about their relationship to other subjects in graph theory. We investigated many approaches to find a more transparent proof for these theorems and possibly generalizations of them. In many cases we found negative answers: counter-examples and NP-completeness results. For example we show that the weighted and the degree-constrained versions of the well-balanced orientation problem are NP-hard. We also show that it is NP-hard to find a minimum cost feasible odd-vertex pairing or to decide whether two graphs with some common edges have simultaneous well-balanced orientations or not. Nash-Williams´ original approach was to define best-balanced orientations with feasible odd-vertex pairings: we show here that not every best-balanced orientation can be obtained this way. However we prove that in the global case this is true: every smooth k-arc-connected orientation can be obtained through a k-feasible odd-vertex pairing. The aim of this paper is to help to find a transparent proof for the Strong Orientation Theorem. In order to achieve this we propose some other approaches and raise some open questions, too. (c) 2008 Elsevier B.V. All rights reserved

    Towards a new strategy for organic milk marketing in Hungary

    Get PDF
    In Hungary, organic food market has both demand and supply oriented aspects: several times not necessary products are distributed, while the selection and volume of certain products are not satisfactory. Thus, our aim was to develop a coordinated benchmark strategy to increase the trade of organic products. To get more details on the Hungarian organic milk market, we conducted professional deep interviews and simultaneously applied the “mystery shopping” method. Nowadays, the market of organic milk and dairy products is slowly increasing in Hungary, however, there is no available statistical data. In the selection there are mostly Hungarian originated products, but some yoghurt, milk, and butter assortments are imported. Partial responsibility belongs to small sale shops’ habit of risk-avoidance. Without a proper selection of products, stores are unable to satisfy consumers’ needs; thus they focus on pushing certain products to increase demand. According to our results, ‘low price category’, ‘local/regional product’, and ‘prestige product’ strategies with attached in-store marketing elements are able to reverse the effects of an unfavourable marketing process

    Conformal stereotactic radiosurgery treatment: plan evaluation methods and results

    Full text link
    The purpose of our study was the objective evaluation of micro-multileaf collimator (mMLC)-based stereotactic radiosurgery treatment plans. Forty-seven patients, 71 lesions received static beam conformal stereotactic radiosurgery treatment in our institute between November 2005 and June 2008. Target volume and organs at risk were outlined on a MRI-CT image fusion basis. BrainSCAN 5.31 system (BrainLAB AG, Heimstetten, Germany) was used for treatment planning, Elekta Presice TS linear accelerator (Elekta Oncology Systems Ltd, Crawley, UK) and BrainLAB m3 mMLC were used for treatment delivery. An invasive head frame, mounted to the treatment table, was used with four screws for patient head fixation. Treatment plans were analysed with objective parameters, such as conformal index (COIN), homogeneity index (HI), coverage index (CI) and healthy tissue relative overdose factor (HTOF) tools. x2 tests were performed between COIN, HI and the geometrical parameters of the target volume (lesion volume - LV, lesion-organ distance - LOD, lesion deformity index - LDI). Mean value of COIN, HI, HTOF and CI was 0.52 (SD 0.13), 1.16 (SD 0.1), 0.88 (SD 0.53), and 0.94 (SD 0.11), respectively. COIN significantly correlated with (p<0.001 in all three cases), while HI was independent of LV, LOD, LDI (p=0.94; 0.14 and 0.72). COIN is similar, HTOF is less than data from the literature. According to our results geometrical parameters of the target volume (size, location, deformation) significantly influence the COIN, but they have no effect on HI

    On packing spanning arborescences with matroid constraint

    Get PDF
    Let D = (V + s, A) be a digraph with a designated root vertex S. Edmonds’ seminal result (see J. Edmonds [4]) implies that D has a packing of k spanning s-arborescences if and only if D has a packing of k (s, t)-paths for all t ∈ V, where a packing means arc-disjoint subgraphs. Let M be a matroid on the set of arcs leaving S. A packing of (s,t) -paths is called M-based if their arcs leaving S form a base of M while a packing of s-arborescences is called M -based if, for all t ∈ V, the packing of (s, t) -paths provided by the arborescences is M -based. Durand de Gevigney, Nguyen, and Szigeti proved in [3] that D has an M-based packing of s -arborescences if and only if D has an M-based packing of (s,t) -paths for all t ∈ V. Bérczi and Frank conjectured that this statement can be strengthened in the sense of Edmonds’ theorem such that each S -arborescence is required to be spanning. Specifically, they conjectured that D has an M -based packing of spanning S -arborescences if and only if D has an M -based packing of (s,t) -paths for all t ∈ V. In this paper we disprove this conjecture in its general form and we prove that the corresponding decision problem is NP-complete. We also prove that the conjecture holds for several fundamental classes of matroids, such as graphic matroids and transversal matroids. For all the results presented in this paper, the undirected counterpart also holds

    Theoretical Investigation of C_60 IR Spectrum

    Full text link
    A semi-empirical model of the infrared (IR) spectrum of the C60_{60} molecule is proposed. The weak IR-active modes seen experimentally in a C60_{60} crystalline sample are argued to be combination modes caused by anharmonicity. The origin of these 2-mode excitations can be either mechanical (anharmonic interatomic forces) or electrical (nonlinear dipole-moment expansion in normal modes coordinates). It is shown that the electrical anharmonicity model exhibits basic features of the experimental spectrum while nonlinear dynamics would lead to a qualitatively different overall picture.Comment: 17 pages, 5 Postscript figures, Fig. 3 of scanned quality; Accepted to PRB; (Original submission failed for the source file

    Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots

    Full text link
    We report on the impulsive generation of coherent optical phonons in CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe experiments using femtosecond laser pulses were performed by tuning the laser central energy to resonate with the absorption edge of the nanocrystals. We identify two longitudinal optical phonons, one longitudinal acoustic phonon and a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the optical phonons as a function of the laser central energy exhibits a resonance that is well described by a model based on impulsive stimulated Raman scattering. The phases of the coherent phonons reveal coupling between different modes. At low power density excitations, the frequency of the optical coherent phonons deviates from values obtained from spontaneous Raman scattering. This behavior is ascribed to the presence of electronic impurity states which modify the nanocrystal dielectric function and, thereby, the frequency of the infrared-active phonons

    The physics of dynamical atomic charges: the case of ABO3 compounds

    Full text link
    Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge definitions, either static (Mulliken, Bader...) or dynamical (Callen, Szigeti...). It is shown that static and dynamical charges are not driven by the same underlying parameters. A unified treatment of dynamical charges in periodic solids and large clusters is proposed. The origin of the difference between static and dynamical charges is discussed in terms of local polarizability and delocalized transfers of charge: local models succeed in reproducing anomalous effective charges thanks to large atomic polarizabilities but, in ABO3 compounds, ab initio calculations favor the physical picture based upon transfer of charges. Various results concerning barium and strontium titanates are presented. The origin of anomalous Born effective charges is discussed thanks to a band-by-band decomposition which allows to identify the displacement of the Wannier center of separated bands induced by an atomic displacement. The sensitivity of the Born effective charges to microscopic and macroscopic strains is examined. Finally, we estimate the spontaneous polarization in the four phases of barium titanate.Comment: 25 pages, 6 Figures, 10 Tables, LaTe

    Is the orbit of the exoplanet WASP-43b really decaying? TESS and MuSCAT2 observations confirm no detection

    Get PDF
    We thank Dr. S. Hoyer from the Laboratoire d'Astrophysique de Marseille (LAM) in France for the helpful discussions. We also thank the anonymous reviewer for the helpful comments and suggestions. This work was supported by the Erasmus+ grant number 2017-1-CZ01-KA203-035562, by the VEGA grant of the Slovak Academy of Sciences number 2/0031/18, by an ESA PRODEX grant under contracting with the ELTE University, by the GINOP number 2.3.2-15-2016-00003 of the Hungarian National Research, Development and Innovation Office, and by the City of Szombathely under agreement number 67.177-21/2016. This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos Sanchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This work was partly financed by the Spanish Ministry of Economics and Competitiveness through grant number PGC2018098153-B-C31. This work was partly supported by JSPS KAKENHI grant numbers JP17H04574, JP18H01265 and JP18H05439, and JST PRESTO grant number JPMJPR1775. This work was partly supported by Grant-in-Aid for JSPS Fellows, grant number JP20J21872. TP acknowledges support from the Slovak Research and Development Agency - the contract No. APVV-20-0148. MT was supported by MEXT/JSPS KAKENHI grant numbers 18H05442, 15H02063, and 22000005. AC acknowledges financial support from the State Agency for Research of the Spanish MCIU through the `Center of Excellence Severo Ochoa' award for the Instituto de Astrophysics of Andalusia (SEV-2017-0709). We acknowledge funding from the European Research Council under the European Union's Horizon 2020 research and innovation program under grant agreement number 694513.Up to now, WASP-12b is the only hot Jupiter confirmed to have a decaying orbit. The case of WASP-43b is still under debate. Recent studies preferred or ruled out the orbital decay scenario, but further precise transit timing observations are needed to definitively confirm or refute the period change of WASP-43b. This possibility is given by the Transiting Exoplanet Survey Satellite (TESS) space telescope. In this work, we used the available TESS data, multicolour photometry data obtained with the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets 2 (MuSCAT2) and literature data to calculate the period change rate of WASP-43b and to improve its precision, and to refine the parameters of the WASP-43 planetary system. Based on the observed-minus-calculated data of 129 mid-transit times in total, covering a time baseline of about 10 yr, we obtained an improved period change rate of (P)over dot = -0.6 +/- 1.2 ms yr(-1) that is consistent with a constant period well within 1 sigma. We conclude that new TESS and MuSCAT2 observations confirm no detection of WASP-43b orbital decay.Erasmus+ grant 2017-1-CZ01-KA203-035562VEGA grant of the Slovak Academy of Sciences 2/0031/18ESA PRODEX grantELTE UniversityNational Research, Development & Innovation Office (NRDIO) - Hungary 2.3.2-15-2016-00003City of Szombathely 67.177-21/2016National Aeronautics & Space Administration (NASA) NAS 5-26555Gaia Multilateral AgreementSpanish Ministry of Economics and Competitiveness PGC2018098153-B-C31Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) JP17H04574 JP18H01265 JP18H05439JST PRESTO grant JPMJPR1775Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science JP20J21872Slovak Research and Development Agency APVV-20-0148Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) 18H05442 15H02063 22000005State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrophysics of Andalusia SEV-2017-0709European Research Council under the European Union's Horizon 2020 research and innovation program 69451

    Integrated copy number and gene expression analysis detects a CREB1 association with Alzheimer’s disease

    Get PDF
    Genetic variation, both single-nucleotide variations and copy number variations (CNV), contribute to changes in gene expression. In some cases these variations are meaningfully correlated with disease states. We hypothesized that in a genetically heterogeneous disorder such as sporadic Alzheimer's disease (AD), utilizing gene expression as a quantitative trait and CNVs as a genetic marker map within the same individuals in the context of case–control status may increase the power to detect relevant loci. Using this approach an 8-kb deletion was identified that contains a PAX6-binding site on chr2q33.3 upstream of CREB1 encoding the cAMP responsive element-binding protein1 transcription factor. The association of the CNV to AD was confirmed by a case–control association study consisting of the Texas Alzheimer Research and Care Consortium and NIA-LOAD Family Study data sets
    corecore