37,878 research outputs found

    Low-energy diffraction; a direct-channel point of view: the background

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    We argue that at low-energies, typical of the resonance region, the contribution from direct-channel exotic trajectories replaces the Pomeron exchange, typical of high energies. A dual model realizing this idea is suggested. While at high energies it matches the Regge pole behavior, dominated by a Pomeron exchange, at low energies it produces a smooth, structureless behavior of the total cross section determined by a direct-channel nonlinear exotic trajectory, dual to the Pomeron exchange.Comment: 6 pages, 1 figure. Talk presented at the Second International "Cetraro" Workshop & NATO Advanced Research Workshop "Diffraction 2002", Alushta, Crimea, Ukraine, August 31 - September 6, 200

    Karhunen-Lo\`eve expansion for a generalization of Wiener bridge

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    We derive a Karhunen-Lo\`eve expansion of the Gauss process Btg(t)01g(u)dBuB_t - g(t)\int_0^1 g'(u)\,d B_u, t[0,1]t\in[0,1], where (Bt)t[0,1](B_t)_{t\in[0,1]} is a standard Wiener process and g:[0,1]Rg:[0,1]\to R is a twice continuously differentiable function with g(0)=0g(0) = 0 and 01(g(u))2du=1\int_0^1 (g'(u))^2\,d u =1. This process is an important limit process in the theory of goodness-of-fit tests. We formulate two special cases with the function g(t)=2πsin(πt)g(t)=\frac{\sqrt{2}}{\pi}\sin(\pi t), t[0,1]t\in[0,1], and g(t)=tg(t)=t, t[0,1]t\in[0,1], respectively. The latter one corresponds to the Wiener bridge over [0,1][0,1] from 00 to 00.Comment: 25 pages, 1 figure. The appendix is extende

    Design of ternary signals for MIMO identification in the presence of noise and nonlinear distortion

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    A new approach to designing sets of ternary periodic signals with different periods for multi-input multi-output system identification is described. The signals are pseudo-random signals with uniform nonzero harmonics, generated from Galois field GF(q), where q is a prime or a power of a prime. The signals are designed to be uncorrelated, so that effects of different inputs can be easily decoupled. However, correlated harmonics can be included if necessary, for applications in the identification of ill-conditioned processes. A design table is given for q les 31. An example is presented for the design of five uncorrelated signals with a common period N = 168 . Three of these signals are applied to identify the transfer function matrix as well as the singular values of a simulated distillation column. Results obtained are compared with those achieved using two alternative methods

    Evolution of Edge States and Critical Phenomena in the Rashba Superconductor with Magnetization

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    We study Andreev bound states (ABS) and resulting charge transport of Rashba superconductor (RSC) where two-dimensional semiconductor (2DSM) heterostructures is sandwiched by spin-singlet s-wave superconductor and ferromagnet insulator. ABS becomes a chiral Majorana edge mode similar to that in spinless chiral p-wave pairing in topological phase (TP). We clarify that two types of quantum criticality about the topological change of ABS near a quantum critical point (QCP), whether ABS exists at QCP or not. In the former type, ABS has a energy gap and does not cross at zero energy in non-topological phase (NTP). These complex properties can be detected by tunneling conductance between normal metal / RSC junctions.Comment: 5 pages, 6 figure

    Conceptual modelling: Towards detecting modelling errors in engineering applications

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    Rapid advancements of modern technologies put high demands on mathematical modelling of engineering systems. Typically, systems are no longer “simple” objects, but rather coupled systems involving multiphysics phenomena, the modelling of which involves coupling of models that describe different phenomena. After constructing a mathematical model, it is essential to analyse the correctness of the coupled models and to detect modelling errors compromising the final modelling result. Broadly, there are two classes of modelling errors: (a) errors related to abstract modelling, eg, conceptual errors concerning the coherence of a model as a whole and (b) errors related to concrete modelling or instance modelling, eg, questions of approximation quality and implementation. Instance modelling errors, on the one hand, are relatively well understood. Abstract modelling errors, on the other, are not appropriately addressed by modern modelling methodologies. The aim of this paper is to initiate a discussion on abstract approaches and their usability for mathematical modelling of engineering systems with the goal of making it possible to catch conceptual modelling errors early and automatically by computer assistant tools. To that end, we argue that it is necessary to identify and employ suitable mathematical abstractions to capture an accurate conceptual description of the process of modelling engineering systems

    Efficiency optimization in a correlation ratchet with asymmetric unbiased fluctuations

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    The efficiency of a Brownian particle moving in periodic potential in the presence of asymmetric unbiased fluctuations is investigated. We found that there is a regime where the efficiency can be a peaked function of temperature, which proves that thermal fluctuations facilitate the efficiency of energy transformation, contradicting the earlier findings (H. kamegawa et al. Phys. Rev. Lett. 80 (1998) 5251). It is also found that the mutual interplay between asymmetry of fluctuation and asymmetry of the potential may induce optimized efficiency at finite temperature. The ratchet is not most efficiency when it gives maximum current.Comment: 10 pages, 7 figure

    Process and lessons learned in the development of food-based dietary guidelines in Ghana

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    Food-based dietary guidelines (FBDGs) are used, globally, as a tool for promoting awareness of healthy diets and, thereby, to improve dietary behaviour. It is also used as a policy framework for creating a health-promoting food environment. In sub-Saharan Africa, only a few countries have developed FBDGs. In 2016, Ghana commenced the process for developing a national FBDG. Four years down the line, significant progress has been achieved towards developing dietary guidelines for persons living in Ghana. The process for developing Ghana's FBDGs has, generally, follow the plan proposed by the 1998 FAO/WO consultative meeting on development of FBDGs, but with minor deviations. These deviations have been occasioned by the need to adapt the process to accommodate context-relevant circumstances relating to local capacity and financial resources constraints. The first step in developing Ghana’s FBDGs was to set up a national Multisectoral Technical Task Team (MTTT) under the policy direction of the Ministry of Food and Agriculture. Thereafter, an evidence review exercise was carried out, involving systematic review of existing literature, complemented by primary data collection, all aimed at understanding the priority foods, nutrition and health issues to be addressed by recommendations in the FBDGs. The key issues identified in the evidence review were validated by the MTTT and subsequently prioritized using an online survey, as well as a prioritization workshop that convened key stakeholders in nutrition and health in Ghana. Subsequently, the priority issues served as the basis for the crafting of technical recommendations. The aim of this paper is to describe the processes, people, data, and resources that have facilitated progress towards development of Ghana’s FBDGs. The challenges, and limitations of the process, as well as the solutions that have been employed to overcome them, have also been highlighted here. For the benefit of future FBDGs development in Ghana and elsewhere, the key lessons that have been learned in the development of Ghana’s FBDGs have been presented, including lessons on political will, planning and time management, resources, capacity development, and multi-sectoral action.&nbsp

    Extended conjugated microporous polymers for photocatalytic hydrogen evolution from water

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    Conjugated microporous polymers (CMPs) have been used as photocatalysts for hydrogen production from water in the presence of a sacrificial electron donor. The relative importance of the linker geometry, the co-monomer linker length, and the degree of planarisation were studied with respect to the photocatalytic hydrogen evolution rate
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