Shape Stability of the LHC Superconducting Dipole: Mechanical Model and Experimental Investigations

The aim of this work is the study of the geometry of the main superconducting dipole for the Large Hadron Collider from the manufacturing process throughout the pre-operative stages to predict the respect of the tight tolerance, imposed by the beam dynamic, in both nominal and chancy working conditions. Expected and unexpected situations have been approached through the development of dedicate models and tests with the purpose of evaluating their impact on magnet geometry. In our study we used structural models of different complexity for different purposes. For example we used analytical models in conjunction with the cold mass geometry database to simulate the overall effect of individual geometry corrections or to discriminate elastic from inelastic measured deformations. By means of finite element models, instead, we investigated the effect of mechanic loads as induced by road transport, or the effect of electro-magnetic forces arising in working conditions. As the assembly complexity prevents from deducing some of the main mechanical properties we set-up different tests and we evaluated the desired properties from the comparison with analytical or finite element models

Educators, Question Your Level of Cultural Responsiveness

Institutions of higher education are becoming increasingly diverse, while faculty of these institutions generally lack the diversity of the student population they teach. This imbalance necessitates educators implement culturally responsive teaching within their classrooms. The intent of this article is to guide educators in determining whether they practice and implement culturally responsive teaching within their classrooms. To make this examination, I present questions that educators should ask themselves to determine their level of cultural responsiveness. In response, educators should look to investigate their level of cultural competency, analyze social constructions that reflects growth in cultural responsiveness, and verify their transformation as a culturally responsive educator

It\u27s the Right Thing to Do: The Voices of Seven White Culturally Responsive Professors of Education

This study explored the motivation of White educators to become culturally responsive, their processes of transformation and how they transformed self and pedagogy as a result

Comparative Study of Heat Transfer from Nb-Ti and Nb3_3Sn coils to He II

In superconducting magnets, the energy deposited or generated in the coil must be evacuated to prevent temperature rise and consequent transition of the superconductor to the resistive state. The main barrier to heat extraction is represented by the electric insulation wrapped around superconducting cables. In the LHC, insulation improvement is a key point in the development of interaction region magnets and injector chain fast-pulsed magnets for luminosity upgrade; the high heat load of these magnets, in fact, is not compatible with the use of current insulation schemes. We review the standard insulation schemes for Nb-Ti and Nb$_{3}$Sn technology from the thermal point of view. We implement, in an analytical model, the strongly nonlinear thermal resistances of the different coil components including the permeability to superfluid helium of Nb-Ti insulations, measured during the LHC main dipole development. We use such a model to compare Nb-Ti and Nb$_{3}$Sn technologies by taking into account their specific operating margin in different working conditions. Finally, we propose an insulation scheme to enhance the heat transfer capability of Nb-Ti coils

Cable Insulation Scheme to Improve Heat Transfer to Superfluid Helium in Nb-Ti Accelerator Magnets

In superconducting magnets operating at high heat loads as the ones for interaction region of particle colliders or for fast cycling synchrotrons, the limited heat transfer capability of state-of-the-art electrical insulation may constitute a heavy limitation to performance. In the LHC main magnets, Nb-Ti epoxy-free insulation, composed of polyimide tapes, has proved to be permeable to superfluid helium, however the heat flux is rather limited. After a review of the standard insulation scheme for Nb-Ti and of the associated heat transfer mechanisms, we show the existence of a large margin available to improve insulation permeability.We propose a possible way to profit of such a margin in order to increase significantly the maximum heat flux drainable from an all polyimide insulated Nb-Ti coil, as it is used in modern accelerator magnets

Riordan Paths and Derangements

Riordan paths are Motzkin paths without horizontal steps on the x-axis. We establish a correspondence between Riordan paths and $(321,3\bar{1}42)$-avoiding derangements. We also present a combinatorial proof of a recurrence relation for the Riordan numbers in the spirit of the Foata-Zeilberger proof of a recurrence relation on the Schr\"oder numbers.Comment: 9 pages, 2 figure

A Simplified Structural Model for the Analysis of Shape Deformations of the LHC Superconducting Dipole Cold Mass

In superconducting magnets for particle accelerators the mechanical accuracy along the length of the Cold Mass is one of the crucial parameters to guarantee the field quality needed by beam dynamics. This issue is made even more challenging in the twin-aperture LHC superconducting dipole where tolerances in the 0.3-1 mm range shall be obtained over a length of 15 m, for a Cold Mass of about 30 tonnes which, to minimize thermal losses, is supported in three points only. To reach this goal a number of geometrical checks and analyses are carried out at all stages of magnet assembly, handling, installation and operation. In this paper we present the structural model of the dipole based on which the checks and the analysis are performed, the nature of the geometrical imperfections identified and the temporary or permanent shape modifications predicted

Control of the Dipole Cold Mass Geometry at CERN to Optimize LHC Performance

The detailed shape of the 15 m long superconducting LHC dipole cold mass is of high importance as it determines three key parameters: the beam aperture, nominally of the order of 10 beam standard deviations; the connectivity of the beam- and technical lines between magnets; the transverse position of non-linear correctors mounted on the dipole ends. An offset of the latter produces unwanted beam dynamics perturbations. The tolerances are in the order of mm over the length of the magnet. The natural flexibility of the dipole and its mechanical structure allow deformations during handling and transportation which exceed the tolerances. This paper presents the observed deformations of the geometry during handling and various operations at CERN, deformations which are interpreted thanks to a simple mechanical model. These observations have led to a strategy of dipole geometry control at CERN, based on adjustment of the position of its central support (the dipole is supported at three positions, horizontally and vertically) to recover individually or statistically their original shape as manufactured. The implementation of this strategy is discussed, with the goal of finding a compromise between conflicting requirements: quality of the dipole geometry, available resources for corrective actions and magnet installation strategy whereby the geometry tolerances depend on the final magnet position in the machine

Better under stress: Improving bacterial cellulose production by Komagataeibacter xylinus K2G30 (UMCC 2756) using adaptive laboratory evolution

Among naturally produced polymers, bacterial cellulose is receiving enormous attention due to remarkable properties, making it suitable for a wide range of industrial applications. However, the low yield, the instability of microbial strains and the limited knowledge of the mechanisms regulating the metabolism of producer strains, limit the large-scale production of bacterial cellulose. In this study, Komagataeibacter xylinus K2G30 was adapted in mannitol based medium, a carbon source that is also available in agri-food wastes. K. xylinus K2G30 was continuously cultured by replacing glucose with mannitol (2% w/v) for 210 days. After a starting lag-phase, in which no changes were observed in the utilization of mannitol and in bacterial cellulose production (cycles 1-25), a constant improvement of the phenotypic performances was observed from cycle 26 to cycle 30, accompanied by an increase in mannitol consumption. At cycle 30, the end-point of the experiment, bacterial cellulose yield increased by 38% in comparision compared to cycle 1. Furthermore, considering the mannitol metabolic pathway, D-fructose is an intermediate in the bioconversion of mannitol to glucose. Based on this consideration, K. xylinus K2G30 was tested in fructose-based medium, obtaining the same trend of bacterial cellulose production observed in mannitol medium. The adaptive laboratory evolution approach used in this study was suitable for the phenotypic improvement of K. xylinus K2G30 in bacterial cellulose production. Metabolic versatility of the strain was confirmed by the increase in bacterial cellulose production from D-fructose-based medium. Moreover, the adaptation on mannitol did not occur at the expense of glucose, confirming the versatility of K2G30 in producing bacterial cellulose from different carbon sources. Results of this study contribute to the knowledge for designing new strategies, as an alternative to the genetic engineering approach, for bacterial cellulose production