Asymptotic Bethe Ansatz on the GKP vacuum as a defect spin chain: scattering, particles and minimal area Wilson loops

Moving from Beisert-Staudacher equations, the complete set of Asymptotic Bethe Ansatz equations and $S$-matrix for the excitations over the GKP vacuum is found. The resulting model on this new vacuum is an integrable spin chain of length $R=2\ln s$ ($s=$ spin) with particle rapidities as inhomogeneities, two (purely transmitting) defects and $SU(4)$ (residual R-)symmetry. The non-trivial dynamics of ${\cal N}=4$ SYM appears in elaborated dressing factors of the 2D two-particle scattering factors, all depending on the 'fundamental' one between two scalar excitations. From scattering factors we determine bound states. In particular, we study the strong coupling limit, in the non-perturbative, perturbative and giant hole regimes. Eventually, from these scattering data we construct the $4D$ pentagon transition amplitudes (perturbative regime). In this manner, we detail the multi-particle contributions (flux tube) to the MHV gluon scattering amplitudes/Wilson loops (OPE or BSV series) and re-sum them to the Thermodynamic Bubble Ansatz.Comment: 103 pages; typos corrected, references added: journal versio

On the scattering over the GKP vacuum

By converting the Asymptotic Bethe Ansatz (ABA) of ${\cal N}=4$ SYM into non-linear integral equations, we find 2D scattering amplitudes of excitations on top of the GKP vacuum. We prove that this is a suitable and powerful set-up for the understanding and computation of the whole S-matrix. We show that all the amplitudes depend on the fundamental scalar-scalar one.Comment: final version, 14 pages, to appear in Physics Letters

Topology of Scrapbooking : Browsing Through a Space in Constant Transformation

The essay sheds light on the practice of scrapbooking promoting a spatial reflection. Topology is used as a tool for exploration and stimulates an investigation in terms of movement and morphological deformations. The topological references, along with three examples of artist scrapbooking, enable tangent reflections that depict a multifaceted contemporary scrapscape with profound design, cultural, and media value. Scrapbooking emerges as a metamorphic threshold practice between the private and the public, capable of empowering the ephemeral and questioning ever-moving constructions such as culture and identity, both visually and materially

Understanding the underlying mechanisms and the role that pre-harvest horticultural maturity, agronomic factors and growing conditions have on postharvest discolouration in celery

Celery is a foliage crop which is commonly consumed for its fresh stalks, which are sold on the market in various retail formats. Celery is appreciated by consumers for its freshness, bright green colour, crisp texture, low calorific content and health promoting properties. An important problem affecting this crop after harvest is browning at cut ends, which is a physiological “disorder” manifesting with brown/black stains on cut or damaged surfaces. It manifests during handling and processing of vegetables, which is the phase where most of the postharvest damage occurs. Cut-end browning is believed to be due to the activity of two enzymes; polyphenol-oxidase (PPO) and phenylalanine ammonia-lyase (PAL). These two enzymes synergistically act to produce melanins, which are the pigments responsible for the black/brown appearance. This is a relevant economic issue as discoloured celery tends to be rejected by retailers, with negative implications for the growers and the UK fresh produce industry. Postharvest browning is not thought to be due to the activity of fungi or bacteria, yet the blackening of surfaces suggests to customers that the product is decaying. Research has been conducted to understand which postharvest factors can influence browning in celery. It has been shown that the use of controlled atmosphere (Gomez and Artes, 2004), heat shock treatments (Loaiza-Velarde et al., 2003) and postharvest application of high intensity light (Zhan et al., 2013) were effective in reducing incidence of the problem. On the other hand, research on pre-harvest factors is still scarce. The aim of the present work was to: 1-) investigate which agronomic factors can affect the severity of postharvest browning in celery; 2-) provide a better understanding of the underlying physiological and biochemical mechanisms involved in this “disorder”. Results showed that agronomic practices can affect postharvest browning in celery. Harvesting at late maturity stages and irrigating below the normal requirements increased postharvest discolouration in this crop. Additionally, the browning mechanism does not seem to be mediated by ethylene in celery. Further biochemical analysis on phenolic compounds and enzymatic activity (PPO and PAL) need to be performed to provide a better elucidation of the browning reaction in this crop

Spherical clustering of users navigating 360{\deg} content

In Virtual Reality (VR) applications, understanding how users explore the omnidirectional content is important to optimize content creation, to develop user-centric services, or even to detect disorders in medical applications. Clustering users based on their common navigation patterns is a first direction to understand users behaviour. However, classical clustering techniques fail in identifying these common paths, since they are usually focused on minimizing a simple distance metric. In this paper, we argue that minimizing the distance metric does not necessarily guarantee to identify users that experience similar navigation path in the VR domain. Therefore, we propose a graph-based method to identify clusters of users who are attending the same portion of the spherical content over time. The proposed solution takes into account the spherical geometry of the content and aims at clustering users based on the actual overlap of displayed content among users. Our method is tested on real VR user navigation patterns. Results show that our solution leads to clusters in which at least 85% of the content displayed by one user is shared among the other users belonging to the same cluster.Comment: 5 pages, conference (Published in: ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)