Magnetic measurement with coils and wires

Accelerator magnets steer particle beams according to the field integrated along the trajectory over the magnet length. Purpose-wound coils measure these relevant parameters with high precision and complement efficiently point-like measurements performed with Hall plates or NMR probes. The rotating coil method gives a complete two-dimensional description of the magnetic field in a series of normal and skew multipoles. The more recent single stretched wire is a reference instrument to measure field integrals and to find the magnetic axis.Comment: 29 pages, 26 figures, presented at the CERN Accelerator School CAS 2009: Specialised Course on Magnets, Bruges, 16-25 June 2009. For higher-resolution figures see http://cdsweb.cern.ch/record/134099

Pricing of scientific journal and market power

We analyze the empirical relationship between journal prices, their quality measured by their citation counts, their age, as well as conduct of publishers. The database covers 22 scientific fields and over 2600 among the most highly reputed and cited journals in 2003. We show that (a) for-profit journals charge roughly 3 times more than journals run by scientific societies; (b) the number of citations has a positive impact on prices; (c) there are large differences in prices across fields that vary from 1 and 6; these are highly (and positively) correlated with the degree of concentration in the industry.

Field Errors Decay and "Snap-Back" in LHC Model Dipoles

The magnetic field in accelerator magnets decays when the current is kept constant during the particles injection phase, and returns quickly (snaps back) to the original values as soon as ramping is restarted. Here we show results of measurements of the decay of the field errors in 10 m long LHC model dipole magnets. In accordance with previous findings, precycles and stops at intermediate current levels influence the decay. We discuss a possible mechanism causing the decay and snap-back, based on the internal field change in the cable

Experimental Evidence of Boundary Induced Coupling Currents in LHC Prototypes

The field quality of 10 m long LHC dipole models has been measured with short rotating coils to explore its dependence on time and position. Multipoles exhibit a longitudinal periodic variation, with period equal to the twist pitch length. This periodicity is shown here to have at least two components with very different time constants. The amplitude of the component with the shorter time constant, in the range of 100 to 300 s, depends on position and time. Larger amplitudes are measured at early times after a ramp and close to regions with incomplete cable transposition with respect to the non-uniform external field change. As the multipoles periodicity is due to current imbalance in the cables, we attribute the short time scale variations to the presence of space and time decaying boundary induced coupling currents (BICC's) in the cable. An estimate of their value is give

Magnetic Field Quality of Short Superconducting Dipole Model Magnets for LHC

A series of 1-m long, 56 mm aperture dipole models has been built and tested at CERN within the scope of the R&D program for LHC. Here we report a summary of results of warm and cold steady state field measurements in these models, concentrating on the contribution of the coil geometry. The first allowed harmonics are clearly correlated to the coil azimuthal size, and the slope of the correlation can be predicted accurately

The Multipoles Factory: An Element of the LHC Control

The measurements performed at CERN on prototypes and first pre-series main dipole magnets confirm the need of an active control of the Large Hadron Collider to compensate the dynamic field changes during the proton beam injection and acceleration. This control requires in turn an accurate forecast of the magnetic field in the accelerator. We plan to predict the field on the basis of two elements: theoretical field models tailored through the accumulated knowledge of the main magnets during series tests, and an on-line measurement system running on few reference magnets tracking the LHC current cycle. Data coming from this "Multipoles Factory" will result from the fusion of the two sources. Based on this system we foresee to deliver calibration information for pre-defined accelerator cycles as well as real time information for the active control. In this paper we report the conceptual design of the system, and we discuss the features and performance of the models that we have developed for the field forecast

Bio-electromagnetic model of deep brain stimulation

Functional stimulation is one of the most fascinating applications of bioelectromagnetism. It deals with the stimulation of excitable biological tissues by electromagnetic fields. One of its most impressive medical applications is the subthalamic nucleus deep brain stimulation (DBS). It consists in the insertion of an electrode into the deep brain, delivering electric pulses to treat Parkinson's disease and other movement disorders. But despite its wide use throughout the world for almost twenty years, the understanding of the mechanisms of action remains unclear. To help clinicians to better understand the mechanisms of DBS, its limitations and implications from an electrical point of view, electrical models of the head can be used to predict the electric potential distribution generated by the electric pulse. With the development of medical imaging techniques, the information on biological tissues that can be used to build these electrical models has never been so detailed. The diffusion tensor magnetic imaging (DT-MRI) is able to provide the orientation of the fibers within the cerebral tissues. Thus, the high inhomogeneity and anisotropy of the head can be modeled through anisotropic electrical conductivity tensors to set up realistic models of the patient's head. This thesis aims to provide to clinicians an accurate prediction of the potential distribution generated by the electric pulse. With this purpose, a finite element (FE) model is set up using electric conductivity values based on DT-MRI data. Special care has been taken to model more realistic boundary conditions than the ones commonly encountered in literature. A great effort has also been put to model the tissues surrounding the stimulation. The results show that these two aspects are impacting significantly the potential distribution. To predict the neural extent of the stimulation, electrical equivalent models of axons are combined with the obtained potentials. Volume of tissues activated (VTA) are thus obtained. Results show that the VTA are also impacted by the decision on how to model the boundary conditions. They show that the usual choice assumed in literature up to now leads to an overestimation of 30% of the VTA

Portfólio de criação publicitária: organização mitos e análise

Elaboração de um portfólio profissional de publicidade. Propiciar, aos formandos de escolas de comunicação que visam trabalhar em criação publicitária, idéias para organizar e apresentar seu talento da melhor forma. Tornar o portfólio o mais palatável possível para os avaliadores das agências de propaganda, sendo portfólio de criação publicitária uma coletânea de peças e campanhas do criativo que deve representar uma síntese de sua capacidade de trabalho. O trabalho se inicia pela revisão de literatura especializada com apoio em experiência de mercado. Inclui depoimentos de profissionais atuantes nesta área para comparar as opiniões sobre o impacto das peças. O cruzamento dessas informações serve para detectar o que funciona, ou não, no momento da criação do portfólio