Taylor-Lagrange renormalization scheme. Application to light-front dynamics

The recently proposed renormalization scheme based on the definition of field operators as operator valued distributions acting on specific test functions is shown to be very convenient in explicit calculations of physical observables within the framework of light-front dynamics. We first recall the main properties of this procedure based on identities relating the test functions to their Taylor remainder of any order expressed in terms of Lagrange's formulae, hence the name given to this scheme. We thus show how it naturally applies to the calculation of state vectors of physical systems in the covariant formulation of light-front dynamics. As an example, we consider the case of the Yukawa model in the simple two-body Fock state truncation.Comment: 18 pages, 6 figures, introduction changed, corrected typos, to be published in Physical Review

Contact Whiskers for Millimeter Wave Diodes

Several techniques are investigated for making short conical tips on wires (whiskers) used for contacting millimeter-wave Schottky diodes. One procedure, using a phosphoric and chromic acid etching solution (PCE), is found to give good results on 12 microns phosphor-bronze wires. Full cone angles of 60 degrees-80 degrees are consistently obtained, compared with the 15 degrees-20 degrees angles obtained with the widely used sodium hydroxide etch. Methods are also described for cleaning, increasing the tip diameter (i.e. blunting), gold plating, and testing the contact resistance of the whiskers. The effects of the whisker tip shape on the electrical resistance, inductance, and capacitance of the whiskers are studied, and examples given for typical sets of parameters

Estimating turbulent velocities in the elliptical galaxies NGC 5044 and NGC 5813

The interstellar and intra-cluster medium in giant elliptical galaxies and clusters of galaxies is often assumed to be in hydrostatic equilibrium. Numerical simulations, however, show that about 5-30% of the pressure in a cluster is provided by turbulence induced by, for example, the central AGN and merger activity. We aim to put constraints on the turbulent velocities and turbulent pressure in the ICM of the giant elliptical galaxies NGC 5044 and NGC 5813 using XMM-Newton RGS observations. The magnitude of the turbulence is estimated using the Fe XVII lines at 15.01 A, 17.05 A, and 17.10 A in the RGS spectra. At low turbulent velocities, the gas becomes optically thick in the 15.01 A line due to resonant scattering, while the 17 A lines remain optically thin. By comparing the (I(17.05)+I(17.10))/I(15.01) line ratio from RGS with simulated line ratios for different Mach numbers, the level of turbulence is constrained. The measurement is limited by systematic uncertainties in the atomic data, which are at the 20-30% level. We find that the line ratio in NGC 5813 is significantly higher than in NGC 5044. This difference can be explained by a higher level of turbulence in NGC 5044. The high turbulent velocities and the fraction of the turbulent pressure support of >40% in NGC 5044, assuming isotropic turbulence, confirm that it is a highly disturbed system, probably due to an off-axis merger. The turbulent pressure support in NGC 5813 is more modest at 15-45%. The (I(17.05)+I(17.10))/I(15.01) line ratio in an optically thin plasma, calculated using AtomDB v2.0.1, is 2 sigma above the ratio measured in NGC 5044, which cannot be explained by resonant scattering. This shows that the discrepancies between theoretical, laboratory, and astrophysical data on Fe XVII lines need to be reduced to improve the accuracy of the determination of turbulent velocities using resonant scattering.Comment: 11 pages, 5 figures, accepted for publication in A&

PROPERTIES OF HOT NUCLEAR MATTER

The properties of cold and hot nuclear matter are studied in the frame of the Brueckner theory, extended to finite temperature. We limit ourself to the BHF approximation. The basic ingredient is the Paris potential supplemented by the introduction of three-body forces coming from the exchange of π and ρ mesons. Particular attention is paid to one-body properties namely the single-particle energy spectrum, the effective mass and the mean free path. We evaluate and discuss the level density parameter a which is closely related to the calculated entropy. In a first approach, the temperature and density dependence of a two-body properties, the effective interaction, is analysed

Hedgerow agroforestry in England and Wales: increasing width to sequester additional carbon

Hedgerow systems are one of the more prominent agroforestry systems in temperate European agriculture, and the UK has the second largest extent of these in the European Union (Herzog 2000; den Herder et al. 2016). An estimated 456 000 km of hedge in England and Wales has been actively managed (Carey et al. 2008); which limits hedge outward growth, and maintains an effective barrier to livestock (Pollard et al. 1974). This management consists of a short period trimming cycle every 1 - 3 years, and a long period structural restoration cycle, after approximately 40 years growth (Staley et al. 2015). A mechanical flail is used for the short period trimming cycle by 92% of farmers in England and Wales (Britt et al. 2011). Typical ‘Enclosure’ hedges in England and Wales were planted with only hawthorn (Crataegus monogyna), in single, or double rows, from the 16th Century onwards (Maclean 2006). Hawthorn is still the dominant woody species, found within 90% of hedges in England and Wales, but a mix of woody species is common, and blackthorn (Prunus spinosa) is the second most frequent species, found within 50% of these hedges (Barr et al. 2000). The potential for temperate agroforestry to sequester carbon (C), and mitigate rising levels of Green-House Gasses (GHG), is beginning to receive more attention (Udawatta and Jose 2012). Axe et al. (2017) showed the potential to sequester C where wider managed hedges had greater C stocks (t C km-1 ). Allowing such hedges to grow wider from lateral branch growth only, without increasing planting density, may not be the most effective way to accumulate Above Ground Biomass (AGB) C. It also introduces uncertainty in using area C stock values (t C ha-1 ) to estimate AGB C (t C), as this parameter assumes a linear relationship with hedge width. Here new data on the contribution made by blackthorn to AGB C stock, and the correlation between hedge width and t C km-1 , from the pilot study of triennially flailed hedge biomass (Axe et al. 2017), along with supporting evidence on shrub growth in unmanaged hedges (Küppers 1985), is examined to advance how atmospheric C could be sequestered by increasing hedge width

Efficacy of using life design-based counselling for an emerging adult who had suffered parental neglect

This article reports on the value of life design-based counselling for an emerging adult who had experienced parental (emotional) neglect and was now ready to embark on a career. Purposive sampling was used to select an emerging adult who had experienced parental neglect and had entered the workplace stage. Such research in South African education contexts is limited. A QUAL + quan design was used to gather and analyse the data. An intrinsic, descriptive, exploratory intervention case study involving a single individual was the basis of the research. Thematic data analysis (in combination with ATLAS.ti) was conducted to analyse the data, that is, look for themes and subthemes in the data. The intervention enhanced the participant’s career resilience and career adaptability. Exploring her life story for themes and patterns helped her gain new insight into the meaning of her experiences. The intervention enabled her to enter a new chapter in her life from a position of strength and an improved sense of self. Longitudinal studies on the long-term effects of life design-based interventions on groups of emerging adults who had experienced different kinds of parental neglect are needed to determine the longer-term value of the kind of intervention described in this article

A 3D macro-element for Soil-Structure Interaction

This paper presents a 3D non linear interface element able to compute Soil Structure Interaction (SSI). Several approaches exist to take this phenomenon into account: the following work is based on the "macro element" concept and is inspired on the work of (Crémer, 2001). The particularity of the macro element lies in the fact that the movement of the foundation is entirely described by a system of generalised variables (forces and displacements) defined in the foundation centre. The non linear behaviour of the soil is reproduced using the classical theory of plasticity. The failure surface is defined using an adequate overturning mechanism according to the work of (Pecker, 1997). The element is able to simulate the 3D behaviour of a circular rigid shallow foundation under cyclic and dynamic loading considering rocking. It is implemented into FedeasLab, a finite element Matlab toolbox. Comparisons with experimental results under monotonic static (Gottardi et al., 1999), cyclic (TRISEE, 1998), and dynamic conditions (Combescure et al., 2000, CAFEEL-ECOEST/ICONS, 2001) show the good performance of the approach

A macro-element to simulate dynamic soil-structure interaction

International audienceThis paper presents a macro-element to simulate dynamic Soil-Structure Interaction (SSI). This new numerical tool is suitable for dynamic (seismic) loadings on structures with shallow foundations. It takes into account the plasticity of the soil, the uplift of the foundation, P-θ effects and the radiation damping. The foundation is supposed infinitely rigid while its movement is entirely described by a system of global variables (forces and displacements) defined in its center. The nonlinear behavior of the soil and the uplift of the foundation are reproduced using the classical theory of plasticity. Uplift and plasticity are combined using the theory of multi-mechanisms. Failure is described by an interaction diagram of the ultimate bearing capacity of the foundation under combined loads. The performance of the macro-element is validated using the experimental results of the structure Camus IV. Furthermore, a parametric study on the behavior of a seven-story building shows the capability of the macro-element to consider different types of soils. Based on the results obtained it seems now possible to use this approach to investigate numerically the behavior of a wider variety of configurations