Physicien | EPFL Graph Search

Un physicien est un scientifique qui étudie le champ de la physique, c'est-à-dire la science analysant les constituants fondamentaux de l'univers (sur toutes les échelles) et les forces qui les relient. Le mot physicien dérive du grec, qui connaît la nature. Originellement, dans l'Antiquité grecque, les Physiciens étaient les philosophes présocratiques de l'École milésienne, ou plus largement de l'École ionienne. Emplois Les trois principaux employeurs de physiciens professionnels sont les universités, les institutions de recherche et l'industrie. De nombreux physiciens exercent une activité en dehors du champ de la physique dans des activités d'éducation, d'ingénierie, d'informatique ou même de finance. Le prix Nobel de physique récompense des personnes ayant effectués des travaux majeurs en physique. Wilhelm Conrad Röntgen est le premier à l'obtenir en 1901. Marie Curie est la première femme à l'obtenir en 1903, Maria Goeppert-Mayer la deuxième en 1963, et Donna Stric

Data coding tools for color-coded vector nanolithography

Charles Baur, Raphaël Foschia, Sébastien Grange, Andrzej Kulik, Saveen Kumar

We propose and demonstrate the ability and efficiency of using a universal file format for a nanolithography pattern. A problem faced by the physicists working in the field of nanolithography is a lack of a flexible pattern design software (possibly open–source) that could be applied in combination with a broad range of commercial scanning probe microscope (SPM) systems. The current nanolithography software packages are device–specific and not portable. Therefore, it is impossible to make a lithography pattern and share it with fellow physicists working on a networked sub-system. In this paper we describe the software designed to read and interpret a nanolithography pattern stored in a Windows Metafile (WMF) standard graphic format and next to draw it on a substrate using an SPM tip. The nanolithography parameters like height, velocity, feedback force, etc. are coded in the color of the WMF onto the RGB channels of the image establishing a distinct relation between a graphical feature (color) and the used nanolithography scheme (voltage, height, etc.). The concept enables preparation of complex patterns using any standard graphic software and aids an intuitive recognition of the mode and parameters set for a pattern. The advantages of using a WMF over other approaches and the universal scope of the software are discussed.

2004

Electron Spin Resonance Magnetometers for Particle Accelerators

Anthony Jean Beaumont

CERN is the European Organization for Nuclear Research located in Geneva, Switzerland. Its main goal is to explore fundamental physics and it exists primarily to provide physicists the necessary tools for doing this, namely accelerators. These tools bring particles to almost the speed of light and then use them in different experiments. The CERN Accelerator Complex includes a chain of interconnected accelerators allowing the acceleration of charged particles up to 6.5 TeV per beam (for protons) in 2018 by the Large Hadron Collider (LHC). Different types of accelerator exist, but at CERN the most common are the synchrotrons. For those, the magnetic field is synchronous with the beam momentum. Magnetic models cannot be always used to predict the field within the required reproducibility, which may be as low as 10^(-5), due to non-linear effects (eddy currents, saturation and hysteresis). Therefore, most of the CERN's synchrotrons are equipped with a real time magnetic field measurement system, the so called "B-Train". The magnetic field measurement devices are composed of absolute field sensors (called "markers"), field tracking sensors (called "induction coils"), an acquisition system, a control system that calculates the magnetic field from the sensors, and a distribution system that delivers the field value to the users. Due to the configuration of the CERN accelerator chain, if one of the injectors fails, the LHC cannot have beam. Consequently, a huge consolidation program of the real time magnetic measurement systems was launched to guarantee operation in the long term. Thus the markers are critical devices for operations at CERN and must be carefully developed to fulfil the high performance and reliability requirements of the B-Train systems. This thesis propose new designs for electron spin resonance (ESR) field markers. We discuss in details the design, the operation, and performance of the ESR sensors based on resonator and oscillator structures including comparison between paramagnetic and ferrimagnetic samples. We propose four field marker levels at 36 mT, 106 mT, 360 mT and 710 mT that correspond to resonance frequencies of 1GHz, 3GHz, 10GHz and 20 GHz. Those measurement values cover most of the marker level requirements of the CERN accelerators and achieving resolution up to 0.1 nT/Hz^(1/2) for field ramps as fast as 5 T/s and field gradients as strong as 12 T/m. We conclude with measurements validation performed on the Proton Synchrotron (PS) and on the Low Energy Ion Ring (LEIR) accelerators.

EPFL2020

Probable nature of higher-dimensional symmetries underlying mammalian grid-cell activity patterns

Alexander Mathis

Lattices abound in nature—from the crystal structure of minerals to the honey-comb organization of ommatidia in the compound eye of insects. These arrangements provide solutions for optimal packings, efficient resource distribution, and cryptographic protocols. Do lattices also play a role in how the brain represents information? We focus on higher-dimensional stimulus domains, with particular emphasis on neural representations of physical space, and derive which neuronal lattice codes maximize spatial resolution. For mammals navigating on a surface, we show that the hexagonal activity patterns of grid cells are optimal. For species that move freely in three dimensions, a face-centered cubic lattice is best. This prediction could be tested experimentally in flying bats, arboreal monkeys, or marine mammals. More generally, our theory suggests that the brain encodes higher-dimensional sensory or cognitive variables with populations of grid-cell-like neurons whose activity patterns exhibit lattice structures at multiple, nested scales. The brain of a mammal has to store vast amounts of information. The ability of animals to navigate through their environment, for example, depends on a map of the space around them being encoded in the electrical activity of a finite number of neurons. In 2014 the Nobel Prize in Physiology or Medicine was awarded to neuroscientists who had provided insights into this process. Two of the winners had shown that, in experiments on rats, the neurons in a specific region of the brain ‘fired’ whenever the rat was at any one of a number of points in space. When these points were plotted in two dimensions, they made a grid of interlocking hexagons, thereby providing the rat with a map of its environment. However, many animals, such as bats and monkeys, navigate in three dimensions rather than two, and it is not clear whether these same hexagonal patterns are also used to represent three-dimensional space. Mathis et al. have now used mathematical analysis to search for the most efficient way for the brain to represent a three-dimensional region of space. This work suggests that the neurons need to fire at points that roughly correspond to the positions that individual oranges take up when they are stacked as tight as possible in a pile. Physicists call this arrangement a face-centered cubic lattice. At least one group of experimental neuroscientists is currently making measurements on the firing of neurons in freely flying bats, so it should soon be possible to compare the predictions of Mathis et al. with data from experiments.