1,538 research outputs found

    Towards an axiomatization of orderings

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    Ordering;operations research

    An interacting quark-diquark model of baryons

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    A simple quark-diquark model of baryons with direct and exchange interactions is constructed. Spectrum and form factors are calculated and compared with experimental data. Advantages and disadvantages of the model are discussed.Comment: 13 pages, 3 eps-figures, accepted by Phys.Rev. C Rapid Communication

    Consequences of limited sediment supply for long-term evolution of offshore tidal sand waves, a 3D model perspective

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    Field data show that offshore tidal sand waves in areas where sediment supply is limited have different characteristics (shape and dimensions) compared with their counterparts in areas with sufficient sediment supply. So far, only the initial formation of tidal sand waves on a sediment-starved shelf has been studied with a 2DV model that ignores variations along the crests. In this study, a 3D non-linear morphodynamic model is used to investigate the effects of sediment availability on the long-term evolution of offshore tidal sand waves. Overall, the simulated sand waves have characteristics that resemble those of observed sand waves. The mature sand waves that develop in the case of limited sediment supply (i.e., thickness of erodible sediment layer is smaller than the height of sand waves) are more three-dimensional, i.e., having isolated and more irregular crestlines compared with those in the case of sufficient supply. With decreasing sediment supply, sand waves have larger spacings between successive crests, smaller heights and they migrate faster. These differences in the characteristics of the sand waves start to occur once the hard bed underneath the erodible sediment layer is exposed

    Soft-core meson-baryon interactions. II. πN\pi N and K+NK^+ N scattering

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    The πN\pi N potential includes the t-channel exchanges of the scalar-mesons σ\sigma and f_0, vector-meson ρ\rho, tensor-mesons f_2 and f_2' and the Pomeron as well as the s- and u-channel exchanges of the nucleon N and the resonances Δ\Delta, Roper and S_{11}. These resonances are not generated dynamically. We consider them as, at least partially, genuine three-quark states and we treat them in the same way as the nucleon. The latter two resonances were needed to find the proper behavior of the phase shifts at higher energies in the corresponding partial waves. The soft-core πN\pi N-model gives an excellent fit to the empirical πN\pi N S- and P-wave phase shifts up to T_{lab}=600 MeV. Also the scattering lengths have been reproduced well and the soft-pion theorems for low-energy πN\pi N scattering are satisfied. The soft-core model for the K+NK^+ N interaction is an SU_f(3)-extension of the soft-core πN\pi N-model. The K+NK^+ N potential includes the t-channel exchanges of the scalar-mesons a_0, σ\sigma and f_0, vector-mesons ρ\rho, ω\omega and ϕ\phi, tensor-mesons a_2, f_2 and f_2' and the Pomeron as well as u-channel exchanges of the hyperons Λ\Lambda and Σ\Sigma. The fit to the empirical K+NK^+ N S-, P- and D-wave phase shifts up to T_{lab}=600 MeV is reasonable and certainly reflects the present state of the art. Since the various K+NK^+ N phase shift analyses are not very consistent, also scattering observables are compared with the soft-core K+NK^+ N-model. A good agreement for the total and differential cross sections as well as the polarizations is found.Comment: 24 pages, 20 PostScript figures, revtex4, submitted to Phys. Rev.

    Patch behaviour and predictability properties of modelled finite-amplitude sand ridges on the inner shelf

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    The long-term evolution of shoreface-connected sand ridges is investigated with a nonlinear spectral model which governs the dynamics of waves, currents, sediment transport and the bed level on the inner shelf. Wave variables are calculated with a shoaling-refraction model instead of using a parameterisation. The spectral model describes the time evolution of amplitudes of known eigenmodes of the linearised system. Bottom pattern formation occurs if the transverse bottom slope of the inner shelf, β, exceeds a critical value β<sub>c</sub>. For fixed model parameters the sensitivity of the properties of modelled sand ridges to changes in the number (<i>N</i>−1) of resolved subharmonics (of the initially fastest growing mode) is investigated. For any <i>N</i> the model shows the growth and subsequent saturation of the height of the sand ridges. The saturation time scale is several thousands of years, which suggests that observed sand ridges have not reached their saturated stage yet. The migration speed of the ridges and the average longshore spacing between successive crests in the saturated state differ from those in the initial state. Analysis of the potential energy balance of the ridges reveals that bed slope-induced sediment transport is crucial for the saturation process. In the transient stage the shoreface-connected ridges occur in patches. The overall characteristics of the bedforms (saturation time, final maximum height, average longshore spacing, migration speed) hardly vary with <i>N</i>. However, individual time series of modal amplitudes and bottom patterns strongly depend on <i>N</i>, thereby implying that the detailed evolution of sand ridges can only be predicted over a limited time interval. Additional experiments show that the critical bed slope β<sub>c</sub> increases with larger offshore angles of wave incidence, larger offshore wave heights and longer wave periods, and that the corresponding maximum height of the ridges decreases whilst the saturation time increases

    Physical activity knowledge, attitudes and practices of the elderly in Bloemfontein old age homes

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    Background: The aim of this study was to describe physical activity knowledge, attitudes and practices of the elderly in Bloemfontein old age homes. Methods: Three hundred and ninety residents (65 years and older) from 11 Bloemfontein old age homes participated in the study. All participants gave informed oral consent before answering a structured questionnaire. Results: The participants had a good general knowledge of the influence of physical activity on life quality, but had less knowledge of the influence of exercise on cholesterol, diabetes and hypertension. Most of the participants (80.5%) enjoyed exercising and 60% had a positive attitude towards exercise. Most participants (62.8%) felt that they had not received enough information about physical activity from their doctor. Few participants (3.8%) took part in prescribed exercise programmes. Conclusions: The participants had a positive attitude towards physical activity, but lacked sufficient knowledge of the practice of physical fitness to be able to understand adequate physical fitness programmes. Elderly people who do not exercise because of a specific health problem may be motivated to exercise in a way that improves quality of life. SA Fam Pract 2004;46(8): 17-1

    Masculine generic pronouns as a gender cue in generic statements

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    An eye-tracking experiment was conducted with speakers of Dutch (N = 84, 36 male), a language that falls between grammatical and natural-gender languages. We tested whether a masculine generic pronoun causes a male bias when used in generic statements—that is, in the absence of a specific referent. We tested two types of generic statements by varying conceptual number, hypothesizing that the pronoun zijn “his” was more likely to cause a male bias with a conceptually singular than a conceptually plural ante-cedent (e.g., Someone (conceptually singular)/Everyone (conceptually plural) with perfect pitch can tune his instrument quickly). We found male participants to exhibit a male bias but with the conceptually singular antecedent only. Female participants showed no signs of a male bias. The results show that the generically intended masculine pronoun zijn “his” leads to a male bias in conceptually singular generic contexts but that this further depends on participant gender

    Pertinent Dirac structure for QCD sum rules of meson-baryon coupling constants

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    Using general baryon interpolating fields JBJ_B for B=N,Ξ,Σ,B= N, \Xi, \Sigma, without derivative, we study QCD sum rules for meson-baryon couplings and their dependence on Dirac structures for the two-point correlation function with a meson i\int d^4x e^{iqx} \bra 0|{\rm T}[J_B(x)\bar{J}_B(0)] |{\cal M}(p)\ket. Three distinct Dirac structures are compared: iγ5i\gamma_5, i\gamma_5\fslash{p}, and γ5σμνqμpν\gamma_5\sigma_{\mu\nu}q^\mu p^\nu structures. From the dependence of the OPE on general baryon interpolating fields, we propose criteria for choosing an appropriate Dirac structure for the coupling sum rules. The γ5σμνqμpν\gamma_5\sigma_{\mu\nu}q^\mu p^\nu sum rules satisfy the criteria while the iγ5i\gamma_5 sum rules beyond the chiral limit do not. For the i\gamma_5\fslash{p} sum rules, the large continuum contributions prohibit reliable prediction for the couplings. Thus, the γ5σμνqμpν\gamma_5\sigma_{\mu\nu}q^\mu p^\nu structure seems pertinent for realistic predictions. In the SU(3) limit, we identify the OPE terms responsible for the F/DF/D ratio. We then study the dependence of the ratio on the baryon interpolating fields. We conclude the ratio F/D0.60.8F/D \sim 0.6-0.8 for appropriate choice of the interpolating fields.Comment: To be published in Phys.Rev.C ; 21 pages,8 figures, revtex ; references are adde