Power-like corrections and the determination of the gluon distribution

Power-suppressed corrections to parton evolution may affect the theoretical accuracy of current determinations of parton distributions. We study the role of multigluon-exchange terms in the extraction of the gluon distribution for the Large Hadron Collider (LHC). Working in the high-energy approximation, we analyze multi-gluon contributions in powers of 1/Q^2. We find a moderate, negative correction to the structure function's derivative d F_2 / d \ln Q^2, characterized by a slow fall-off in the region of low to medium Q^2 relevant for determinations of the gluon at small momentum fractions

An innovative navigation and guidance system for small unmanned aircraft using low-cost sensors

Purpose - The purpose of this paper is to design a compact, light and relatively inexpensive navigation and guidance system capable of providing the required navigation performance (RNP) in all phases of flight of small unmanned aircrafts (UA), with a special focus on precision approach and landing. Design/methodology/approach - Two multi-sensor architectures for navigation and guidance of small UA are proposed and compared in this paper. These architectures are based, respectively, on a standard extended Kalman filter (EKF) approach and a more advanced unscented Kalman filter (UKF) approach for data fusion of global navigation satellite systems (GNSS), micro-electro-mechanical system (MEMS)-based inertial measurement unit (IMU) and vision-based navigation (VBN) sensors. Findings - The EKF-based VBN-IMU-GNSS-aircraft dynamics model (ADM) (VIGA) system and the UKF-based system (VIGA+) performances are compared in a small UA integration scheme (i.e. AEROSONDE UA platform) exploring a representative cross-section of this UA operational flight envelope, including high-dynamics manoeuvres and CAT-I to CAT-III precision approach tasks. The comparison shows that the position and attitude accuracy of the proposed VIGA and VIGA+ systems are compatible with the RNP specified in the various UA flight profiles, including precision approach down to CAT-II. Originality/value - The novelty aspect is the augmentation by ADM in both architectures to compensate for the MEMS-IMU sensor shortcomings in high-dynamics attitude determination tasks. Additionally, the ADM measurements are pre-filtered by an UKF with the purpose of increasing the ADM attitude solution stability time in the UKF-based system

Three-loop corrections to the soft anomalous dimension in multi-leg scattering

We present the three-loop result for the soft anomalous dimension governing long-distance singularities of multi-leg gauge-theory scattering amplitudes of massless partons. We compute all contributing webs involving semi-infinite Wilson lines at three loops and obtain the complete three-loop correction to the dipole formula. We find that non-dipole corrections appear already for three coloured partons, where the correction is a constant without kinematic dependence. Kinematic dependence appears only through conformally-invariant cross ratios for four coloured partons or more, and the result can be expressed in terms of single-valued harmonic polylogarithms of weight five. While the non-dipole three-loop term does not vanish in two-particle collinear limits, its contribution to the splitting amplitude anomalous dimension reduces to a constant, and it only depends on the colour charges of the collinear pair, thereby preserving strict collinear factorization properties. Finally we verify that our result is consistent with expectations from the Regge limit.Comment: v2: remaining diagrams computed; colour conservation accounted for; strict collinear factorization shown to hold. Some references added. 6 pages, 2 figure

Factorization Properties of Soft Graviton Amplitudes

We apply recently developed path integral resummation methods to perturbative quantum gravity. In particular, we provide supporting evidence that eikonal graviton amplitudes factorize into hard and soft parts, and confirm a recent hypothesis that soft gravitons are modelled by vacuum expectation values of products of certain Wilson line operators, which differ for massless and massive particles. We also investigate terms which break this factorization, and find that they are subleading with respect to the eikonal amplitude. The results may help in understanding the connections between gravity and gauge theories in more detail, as well as in studying gravitational radiation beyond the eikonal approximation.Comment: 35 pages, 5 figure

Pairing micropollutants and clay-composite sorbents for efficient water treatment: Filtration and modeling at a pilot scale

Organically modified clay minerals have been widely developed, tested and employed as sorbents for organic pollutants. However, the process of pollutant-composite pairing is not commonly addressed, which would be valuable for efficient pollutant filtration by such sorbents. This study presents an approach for achieving efficient pollutant removal by large-scale composite filters, based on pairing chemically compatible pollutants and composites and by employing a predictive filtration model. The removal of three organic pollutants, simazine, sulfentrazone and diclofenac by lab-scale filtration columns containing one of three sorbents, a polymer-, micelle- or liposome-clay composite, was measured. Understanding the factors governing pollutant-organic modifier interactions enabled to pair an efficient sorbent to each pollutant. The high removal (80%) of simazine by the polymer composite, was attributed to hydrogen bonds andu-n interactions, compared to less than 20% removal by the surfactant composites. The removal of the anionic diclofenac (pKa = 4.1) was mainly governed by electrostatic attraction, explaining its high removal by the most positively charge sorbent, the liposome composite. Sulfentrazone (pKa = 6.5) removal was mostly affected by micellar solubilization and upon its removal, the zeta potential of the micelle-composite was not reduced as obtained for diclofenac removal. The filtration of the successful pairs was modelled to determine sorbent capacity and adsorption and desorption rate constants. The pilot filtration experiments were well described by the model and demonstrated efficient removal of paired pollutants and sorbents. Model simulations predicted promising treatment at environmental pollutant concentrations in the lag L-1 range. This pairing approach along with model calculations can be a strong and valid tool for efficient pollutant-sorbent filtration

A novel series solution to the renormalization group equation in QCD

Recently, the QCD renormalization group (RG) equation at higher orders in MS-like renormalization schemes has been solved for the running coupling as a series expansion in powers of the exact 2-loop order coupling. In this work, we prove that the power series converges to all orders in perturbation theory. Solving the RG equation at higher orders, we determine the running coupling as an implicit function of the 2-loop order running coupling. Then we analyze the singularity structure of the higher order coupling in the complex 2-loop coupling plane. This enables us to calculate the radii of convergence of the series solutions at the 3- and 4-loop orders as a function of the number of quark flavours $n_{\rm f}$. In parallel, we discuss in some detail the singularity structure of the ${\bar{\rm MS}}$ coupling at the 3- and 4-loops in the complex momentum squared plane for $0\leq n_{\rm f} \leq 16$. The correspondence between the singularity structure of the running coupling in the complex momentum squared plane and the convergence radius of the series solution is established. For sufficiently large $n_{\rm f}$ values, we find that the series converges for all values of the momentum squared variable $Q^2=-q^2>0$. For lower values of $n_{\rm f}$, in the ${\bar{\rm MS}}$ scheme, we determine the minimal value of the momentum squared $Q_{\rm min}^2$ above which the series converges. We study properties of the non-power series corresponding to the presented power series solution in the QCD Analytic Perturbation Theory approach of Shirkov and Solovtsov. The Euclidean and Minkowskian versions of the non-power series are found to be uniformly convergent over whole ranges of the corresponding momentum squared variables.Comment: 29 pages,LateX file, uses IOP LateX class file, 2 figures, 13 Tables. Formulas (4)-(7) and Table 1 were relegated to Appendix 1, some notations changed, 2 footnotes added. Clarifying discussion added at the end of Sect. 3, more references and acknowledgments added. Accepted for publication in Few-Body System

New tsunami damage functions developed in the framework of SCHEMA project: application to European-Mediterranean coasts

In the framework of the European SCenarios for tsunami Hazard-induced Emergencies MAnagement (SCHEMA) project (<a href="http://www.schemaproject.org" target_"blank">www.schemaproject.org</a>), we empirically developed new tsunami damage functions to be used for quantifying the potential tsunami damage to buildings along European-Mediterranean coasts. <br><br> Since no sufficient post-tsunami observations exist in the Mediterranean areas, we based our work on data collected by several authors in Banda Aceh (Indonesia) after the 2004 Indian Ocean tsunami. Obviously, special attention has been paid in focusing on Indonesian buildings which present similarities (in structure, construction material, number of storeys) with the building typologies typical of the European-Mediterranean areas. <br><br> An important part of the work consisted in analyzing, merging, and interpolating the post-disaster observations published by three independent teams in order to obtain the spatial distribution of flow depths necessary to link the flow-depth hazard parameter to the damage level observed on buildings. Then we developed fragility curves (showing the cumulative probability to have, for each flow depth, a damage level equal-to or greater-than a given threshold) and damage curves (giving the expected damage level) for different classes of buildings. It appears that damage curves based on the weighted mean damage level and the maximum flow depth are the most appropriate for producing, under GIS, expected damage maps for different tsunami scenarios

From Webs to Polylogarithms

We compute a class of diagrams contributing to the multi-leg soft anomalous dimension through three loops, by renormalizing a product of semi-infinite non-lightlike Wilson lines in dimensional regularization. Using non-Abelian exponentiation we directly compute contributions to the exponent in terms of webs. We develop a general strategy to compute webs with multiple gluon exchanges between Wilson lines in configuration space, and explore their analytic structure in terms of $\alpha_{ij}$, the exponential of the Minkowski cusp angle formed between the lines $i$ and $j$. We show that beyond the obvious inversion symmetry $\alpha_{ij}\to 1/\alpha_{ij}$, at the level of the symbol the result also admits a crossing symmetry $\alpha_{ij}\to -\alpha_{ij}$, relating spacelike and timelike kinematics, and hence argue that in this class of webs the symbol alphabet is restricted to $\alpha_{ij}$ and $1-\alpha_{ij}^2$. We carry out the calculation up to three gluons connecting four Wilson lines, finding that the contributions to the soft anomalous dimension are remarkably simple: they involve pure functions of uniform weight, which are written as a sum of products of polylogarithms, each depending on a single cusp angle. We conjecture that this type of factorization extends to all multiple-gluon-exchange contributions to the anomalous dimension.Comment: 64 pages, 8 figure