Beam Cleaning and Collimation Systems

Collimation systems in particle accelerators are designed to dispose of unavoidable losses safely and efficiently during beam operation. Different roles are required for different types of accelerator. The present state of the art in beam collimation is exemplified in high-intensity, high-energy superconducting hadron colliders, like the CERN Large Hadron Collider (LHC), where stored beam energies reach levels up to several orders of magnitude higher than the tiny energies required to quench cold magnets. Collimation systems are essential systems for the daily operation of these modern machines. In this document, the design of a multistage collimation system is reviewed, taking the LHC as an example case study. In this case, unprecedented cleaning performance has been achieved, together with a system complexity comparable to no other accelerator. Aspects related to collimator design and operational challenges of large collimation systems are also addressed.Comment: 35 pages, contribution to the 2014 Joint International Accelerator School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14 Nov 201

Hierarchical nanomechanics of collagen microfibrils

Collagen constitutes one third of the human proteome, providing mechanical stability, elasticity and strength to connective tissues. Collagen is also the dominating material in the extracellular matrix (ECM) and is thus crucial for cell differentiation, growth and pathology. However, fundamental questions remain with respect to the origin of the unique mechanical properties of collagenous tissues, and in particular its stiffness, extensibility and nonlinear mechanical response. By using x-ray diffraction data of a collagen fibril reported by Orgel et al. (Proceedings of the National Academy of Sciences USA, 2006) in combination with protein structure identification methods, here we present an experimentally validated model of the nanomechanics of a collagen microfibril that incorporates the full biochemical details of the amino acid sequence of the constituting molecules. We report the analysis of its mechanical properties under different levels of stress and solvent conditions, using a full-atomistic force field including explicit water solvent. Mechanical testing of hydrated collagen microfibrils yields a Young’s modulus of ≈300 MPa at small and ≈1.2 GPa at larger deformation in excess of 10% strain, in excellent agreement with experimental data. Dehydrated, dry collagen microfibrils show a significantly increased Young’s modulus of ≈1.8 to 2.25 GPa (or ≈6.75 times the modulus in the wet state) owing to a much tighter molecular packing, in good agreement with experimental measurements (where an increase of the modulus by ≈9 times was found). Our model demonstrates that the unique mechanical properties of collagen microfibrils can be explained based on their hierarchical structure, where deformation is mediated through mechanisms that operate at different hierarchical levels. Key mechanisms involve straightening of initially disordered and helically twisted molecules at small strains, followed by axial stretching of molecules, and eventual molecular uncoiling at extreme deformation. These mechanisms explain the striking difference of the modulus of collagen fibrils compared with single molecules, which is found in the range of 4.8±2 GPa or ≈10-20 times greater. These findings corroborate the notion that collagen tissue properties are highly scale dependent and nonlinear elastic, an issue that must be considered in the development of models that describe the interaction of cells with collagen in the extracellular matrix. A key impact the atomistic model of collagen microfibril mechanics reported here is that it enables the bottom-up elucidation of structure-property relationships in the broader class of collagen materials such as tendon or bone, including studies in the context of genetic disease where the incorporation of biochemical, genetic details in material models of connective tissue is essential

Atlas de la a-gentrificación : políticas para la sostenibilidad social en las transformaciones urbanas en ciudades europeas

La ciudad es esa dimensión territorial y social en la que vivimos buena parte de los europeos. Se trata de una estructura urbana que tiene sus raícesen la Polis griega, donde se daba la coincidencia entre Estado y Ciudad, donde cada ciudadano era político, es decir participaba activamente de lasdecisiones colectivas. Europa —en la historia y en la actualidad— es la suma de diferentes identidades que comparten el mismo espacio y el mismocurso de tiempo: “el equilibrio europeo” es una realidad dinámica que busca “el carácter unitario de una magnífica pluralidad” (Ortega y Gasset, 1966).La ciudad es esa dimensión territorial y social en la que vivimos buena parte de los europeos. Se trata de una estructura urbana que tiene sus raícesen la Polis griega, donde se daba la coincidencia entre Estado y Ciudad, donde cada ciudadano era político, es decir participaba activamente de lasdecisiones colectivas. Europa —en la historia y en la actualidad— es la suma de diferentes identidades que comparten el mismo espacio y el mismocurso de tiempo: “el equilibrio europeo” es una realidad dinámica que busca “el carácter unitario de una magnífica pluralidad” (Ortega y Gasset, 1966)

A. Romeo, Orfeo in Ovidio: La creazione di un nuovo epos (Studi di Filologia Antica e Moderna 25), Rubbettino Editore, Soveria Mannelli 2012

Nello spazio tra i libri X e XI delle Metamorfosi, quel "volo" lungo e complesso che è il carmen orfico rappresenta uno snodo di fondamentale importanza per la comprensione dell'intero poema ovidiano. Alessandra Romeo, docente di letteratura Latina presso l'Università della Calabria dedica questa monografia a un tema da lei già esplorato da qualche anno a questa parte in alcuni studi preparatori. Se a un primo approccio il libro ci risulta caratterizzato da un italiano bello ma molto erudito, svolto in periodi complessi e ricchi di tecnicismi che limitano l'accesso a un pubblico specializzato, il fascino dell'argomento e la profonda, ammirevole preparazione della studiosa finiscono per "legarci" al testo, abituandoci al suo stile e regalandoci notevoli sfumature di due importanti libri delle Metamorfos

Resonant and random excitations on the proton beam in the Large Hadron Collider for active halo control with pulsed hollow electron lenses

We present the results of numerical simulations and experimental studies about the effects of resonant and random excitations on proton losses, emittances, and beam distributions in the Large Hadron Collider (LHC). In addition to shedding light on complex nonlinear effects, these studies are applied to the design of hollow electron lenses (HEL) for active beam halo control. In the High-Luminosity Large Hadron Collider (HL-LHC), a considerable amount of energy will be stored in the beam tails. To control and clean the beam halo, the installation of two hollow electron lenses, one per beam, is being considered. In standard electron-lens operation, a proton bunch sees the same electron current at every revolution. Pulsed electron beam operation (i.e., different currents for different turns) is also considered, because it can widen the range of achievable halo removal rates. For an axially symmetric electron beam, only protons in the halo are excited. If a residual field is present at the location of the beam core, these particles are exposed to time-dependent transverse kicks and to noise. We discuss the numerical simulations and the experiments conducted in 2016 and 2017 at injection energy in the LHC. The excitation patterns were generated by the transverse feedback and damping system, which acted as a flexible source of dipole kicks. Proton beam losses, emittances, and transverse distributions were recorded as a function of excitation patterns and strengths. The resonant excitations induced rich dynamical effects and nontrivial changes of the beam distributions, which, to our knowledge, have not previously been observed and studied in this detail. We conclude with a discussion of the tolerable and achievable residual fields and proposals for further studies.Comment: 33 pages, 32 figures, 46 references. Revised manuscript submitted to Phys. Rev. Accel. Beam

C. Ricci, Soldati e veterani nella vita cittadina dell'Italia imperiale (Urbana Species. Vita di città nell'Italia e nell'Impero romano, 1), Roma 2010

In che misura e con quali modalità soldati semplici e veterani dell'esercito romano in età imperiale, tra I sec. a. C. e III sec. d. C., partecipavano alla vita sociale e politica delle città da cui provenivano o in cui sceglievano di stabilirsi? Questo è l'interrogativo che muove la ricerca di Cecilia Ricci, studiosa, ora docente di Storia Romana ed Epigrafia presso l'Università degli Studi del Molise, che da anni si dedica a temi quali le truppe urbane in epoca imperiale e il loro rapporto con i civili, gli usi funerari nel mondo romano e la presenza degli stranieri a Roma in età imperiale. Soldati e veterani nella vita cittadina dell'Italia imperiale, edito da Quasar nel 2010 e inserito nella collana Urbana Species. Vita di città nell'Italia e nell'Impero romano, è un breve volume frutto, come emerge dall'accuratezza nell'elaborazione, di un notevole lavoro di ricerca proposto attraverso una scrittura agile che ne permette una veloce lettura

Determinants of international emergency aid - humanitarian need only ?

The authors use an original data set covering more than 400 recent natural disasters to analyze the determinants of international emergency aid. Although humanitarian need is a major determinant of emergency relief payments, the results imply that political and strategic factors play a crucial role in the emergency aid allocation. On average, donor governments favor smaller, geographically closer, and oil exporting countries, and display significant biases in favor of politically less aligned countries as well as toward their former colonies. The authors also test and reject the independence of donors'aid decisions, finding strong evidence for bandwagon effects in humanitarian assistance.Hazard Risk Management,Natural Disasters,Disaster Management,Gender and Health,Development Economics&Aid Effectiveness