Real-time control of beam parameters

This article gives an overview of the theory and application of real-time control of accelerator beams. The design and structure of orbit feedbacks are described, going from basic local feedbacks to modern state-of-the art global systems. The time domain behaviour is analysed for the building blocks of the systems as well as from the spectrum of random sources driving the orbit perturbations. The use of predictive ltering is shown for the design of the control algorithm. A second important class is the control of tunes and chromaticities. Advanced tune measurements are performed using a digital phase-locked loop. The feedback systems are typically hybrid, simultaneously working on tune and coupling and chromaticity. Adaptive feed-forward algorithms are shown to be a suitable approach for use in energy ramping. For application in a high-speed bunch-by-bunch feedback system, ef cient low-noise data processing is presented for a digital lter. Also here, predictive ltering is shown to give well-adapted high-order lters

Modeling a 30 GHz waveguide loaded detuned structure for the compact linear collider (CLIC)

One of the major challenges in designing a multi bunch structure for the Compact Linear Collider Study CLIC are the long range transverse wake fields, which couple the transverse motion of adjacent bu nches and lead to instabilities. To the most part, possible solutions, which suppress the long range wake, require a mechanical precision, which is difficult to achieve for the high fundamental freque ncy of 30 GHz. A possible way out of this dilemma consists of combining a loose detuning with the strong damping provided by radial waveguide loads. For this type of structure, an equivalent circuit m odel has been developed, which simulates the behavior of the total structure for the lower two dipole bands. The circuit parameters are derived from the results of numerical field calculations. Mismat ch of the waveguide loads is incorporated in the circuit model via a table of scattering parameters. Using this model, a first 'skeleton' design has been done. Requiring only a limited performance of the waveguide loads, this design shows a sufficient suppression of the transverse long range wakes

Seawater transfer alters the intestinal microbiota profiles of Atlantic salmon (Salmo salar L.)

This study was funded by a BBSRC Eastbio PhD studentship to CED and BBSRC grant BB/M026604/1. The authors wish to thank Ana Rita Sancho Silva for facilitating the sampling for the experiment. Furthermore we would like to express our gratitude to Ian and Alastair Fraser for their support at the SFF fish farms on the Isle of Mull.Peer reviewedPublisher PD

Design of a RF Gun for Heavy Beam Loading

For the drive beam generation of the CLIC Test Facility, a RF photo electron gun is required to generate a charge of 1 uC in a train of 48 bunches. The extracted beam energy of 6.5 J leads to a pronounced decrease of the field gradient, causing strong variations in the transverse and longitudinal beam dynamics. The drop in beam momentum yields a variation in focusing of the following solenoid leading to a blow-up of the transversal emittance. A second effect is the change of the bunch spacing caused by differing bunch velocities. These effects are to a large extent determined by the beam loading in the first cell, which contains the photo cathode. In order to reduce this effect with moderate expense of RF power, a new gun design has been developed using a TM02 resonance in the first cell followed by two standard TM01 cells. Beam simulations show that with this gun, the overall change in the longitudinal bunch spacing can be strongly reduced. Also the chromatic effects in the solenoid due to the drop in longitudinal momentum are partially compensated

CLIC Waveguide Damped Accelerating Structure Studies

Studies of waveguide damped 30 GHz accelerating structures for multibunching in CLIC are described. Frequency discriminated damping using waveguides with a lowest cutoff frequency above the fundamental but below the higher order modes was considered. The wakefield behavior was investigated using time domain MAFIA computations over up to 20 cells and for frequencies up to 150 GHz. A configuration consisting of four T-cross-sectioned waveguides per cell reduces the transverse wake below 1% at typical CLIC bunch spacings

Connecting Cape Breton Island and Newfoundland, Canada: Geophysical Modeling of pre-Carboniferous 'Basement' Rocks in the Cabot Strait Area

Magnetic and gravity data from northeastern Cape Breton Island, southwestern Newfoundland, and the intervening Cabot Strait area were compiled and used to generate a series of maps displaying magnetic (filtered total field, first and second derivative) and gravity (Bouguer anomaly onshore, free-air anomaly offshore) information to enhance the anomaly pattern associated with regional geology. With further constraints from previously published seismic reflection interpretations and detailed maps of onshore geology, five two-dimensional subsurface models were generated.  Potential field anomalies in the offshore can be correlated with onshore faults, rock units, and pre-Carboniferous terranes.  In Newfoundland, the Cabot – Long Range Fault separates Grenvillian basement to the northwest from peri-Gondwanan Port aux Basques subzone basement in the southeast and can be traced to the Wilkie Brook Fault on Cape Breton Island.  The Cape Ray Fault/Red Indian Line merges offshore with the Cabot – Long Range Fault so that Notre Dame subzone rocks do not extend across the Cabot Strait area.  The Port aux Basques – Exploits subzone boundary crosses the strait but is likely buried by younger rocks onshore in Cape Breton Island.  Magnetic halos in the Exploits subzone are probably caused by Silurian – Devonian plutons like those in the Burgeo Intrusive Suite. The Exploits – Bras d’Or terrane boundary is located within the Ingonish magnetic anomaly, which was resolved into four overlapping components representing basement sources intruded into metasedimentary rocks and dioritic and granodioritic plutons of the Bras d’Or terrane.  The Bras d’Or terrane can be traced to the Cinq-Cerf block and Grey River areas in southern Newfoundland.  The interpretations suggest that Bras d’Or terrane ‘basement’ may underlie all of Exploits subzone, and that the Aspy terrane of Cape Breton Island is part of that subzone. SOMMAIRELes données magnétométriques et gravimétriques du nord-est de l’île du Cap-Breton, dans le sud-ouest de Terre-Neuve, et de la région du détroit de Cabot contigu, ont été compilées et utilisées pour produire une série de cartes affichant les particularités magnétiques (champ total filtré, dérivé première et seconde) et gravimétriques (anomalie de Bouguer de la côte, anomalie à l’air libre extracôtière) pour ajouter à la compréhension des motifs d’anomalie de la géologie régionale.  En tenant compte des limitations imposées par les interprétations de données de levés de sismique réflexion déjà publiées et de cartes détaillées de géologie continentale, cinq modèles 2D du sous-sol ont été produits.  Des anomalies de champ potentiel en zone extracôtière peuvent être corrélées avec des failles, des unités lithologiques et des terranes pré-carbonifères sur la côte.   Sur l’île de Terre-Neuve, la faille de Cabot-Long Range qui sépare le socle grenvillien au nord-ouest de la sous-zone de socle péri-gondwanienne, de Port-aux- Basques au sud-est, peut être reliée à la faille de Wilkie Brook sur l’île du Cap-Breton.  La faille du Cap Ray et la linéation de Red Indian se fondent au large avec la faille de Cabot – Long  Range, ce qui signifie que les roches de la sous-zone de Notre-Dame ne traversent pas la région du détroit de Cabot.  La limite de la sous-zone de Port aux Basques-Exploits traverse le détroit, mais elle est vraisemblablement enfouie sous des roches plus jeunes sur l’île du Cap-Breton.  Les halos magnétiques dans la sous-zone Exploits sont probablement causés par des plutons siluro-dévoniens comme c’est le cas de ceux de la séquence intrusive de Burgeo.  La limite du terrane Exploits-Bras d’Or est située dans l’anomalie magnétique Ingonish, laquelle s’est révélée être constituée de quatre composantes superposées représentant des sources de socle engoncées dans des roches métasédimentaires, et dans des plutons dioritiques et granodioritiques du terrane de Bras d’Or.  On peut suivre le terrane de Bras d’Or jusque dans les régions du bloc de Cinq-Cerf et de Grey River dans le sud de Terre-Neuve.  Les interprétations permettent de penser que le « socle » du terrane de Bras d’Or pourrait constituer l’assise rocheuse de la sous-zone Exploits, et que le terrane Aspy de l’île du Cap-Breton ferait partie de cette sous-zone

Transpressive dextral shear in the Italva-Itaperuna section, Northern State of Rio de Janeiro, Brazil

Structural analysis carried out on a segment of the Neoproterozoic Ribeira Belt, southeastern Brazil, show that it represents part of the transpressive dextral orogen related to the Central Mantiqueira Province. NNE-trending and steeply dipping regional mylonitic belts form anastomosed geometry, and describe a map-scale, S-C-like structure that is characterized by their deflection towards NE near the Além Paraíba Lineament. Lithological and structural control related to deformation partition were responsible for the formation of felsic mylonitic granulites with S-type granites lenses developed in ductile shear zones, alternated with less deformed intermediate to basic granulites associated with charnockites. The dextral shear sense indicators are consistent with transpressive deformation in the region and are common especially at the border of the main shear zones. The presence of S-type leucogranite may lead to variations of linear and planar relationships, which result in local extension zones. These elements are consistent with oblique continental collision considering the São Francisco Craton as a stable block.A análise estrutural efetuada num segmento neoproterozóico do Cinturão Ribeira, Sudeste do Brasil, mostra que ele representa parte do orógeno transpressivo destral, relacionado com a Província Mantiqueira Central. Caracteriza-se regionalmente por um cinturão milonítico de direção NNE e mergulhos subverticais, com geometria anastomosada, descrevendo em escala de mapa estruturas do tipo S-C, que são defletidas para direção NE nas proximidades do Lineamento de Além-Paraíba. O controle estrutural e litológico e a partição da deformação foram responsáveis pela formação de granulitos miloníticos félsicos com lentes de granitos tipo-S, desenvolvidos em zonas de cisalhamento dúcteis, alternados com granulitos básicos a intermediários menos deformados com charnockitos associados. Na região, os indicadores cinemáticos do cisalhamento simples, destral, são consistentes com a deformação transpressiva, que é particularmente comum nas bordas das zonas de cisalhamento mais importantes. A presença de leucogranitos tipo-S pode levar a variação das relações planares e lineares,as quais condicionam, localmente, zonas extensionais. Estes elementos são consistentes com uma colisão continental oblíqua, considerando o Cráton do São Francisco como um bloco estável

The effects of group membership and task experience on asynchronous computer-mediated group performance, group competencies and group member reactions

Organizations that use computer-mediated communication (CMC) to communicate and coordinate work are ubiquitous and highly dependent on the permeation of virtual work groups throughout the organizational structure. In this era of distributed work, it is imperative to determine which factors affect the efficiency and effectiveness of asynchronous computer-mediated groupwork. Two factors are identified in the literature to potentially mediate effects on asynchronous computer-mediated groupwork: group membership and task experience. The purpose of this study is to investigate the extent to which these factors affect group performance, competencies and group members' social experiences. A 2 x 2 between-subjects factorial design was used to carry out this study. Three-person groups (n = 56) performed tasks corresponding to task types 2 and 4 of McGrath's (1984) circumplex: an idea generation task and a judgment task. The study ran over a period of three weeks via the CMC system FirstClass® . Four treatment conditions were constructed using FirstClass whereby group membership and task experience conditions were created by varying participants' experiences during weeks 1 and 2, prior to the performance of the criterion judgment task at week 3. Results indicated that groups acquiring task experience as stable groups during weeks 1 and 2 performed better on the judgment task at week 3 than groups in other treatment conditions. Analyses also confirmed that membership and task experience had a substantial effect on group competencies and member reactions. Groups with changing membership exchanged a greater amount of communication, with those groups not having acquired judgment task experience during weeks 1 and 2 producing the highest number of process-specific remarks. Participants in stable groups reported higher levels of shared knowledge and awareness of group members' ability. Members of stable groups reported higher levels of group cohesion and collective orientation while those who were in stable groups and acquiring task experience expressed the highest amount of member interdependence. Subjects in stable groups were more satisfied with the task and the process of completing it while those who also acquired task experience were more satisfied and confident in the final task solution. Results are discussed in terms of the implications of structuring asynchronous computer-mediated collaborative work environments in organizations