April 30th, 2020

лошадь, диаграмма, Фейнман

Диагностика пучков - то, что надо!

Начались материалы очередной ЦЕРНовской школы по ускорителям, и как раз то, что мне нужно - диагностика пучков.

Beam Diagnostic Requirements: an Overview: https://arxiv.org/abs/2005.08389
Gero Kube
Beam diagnostics and instrumentation are an essential part of any kind of accelerator. There is a large variety of parameters to be measured for observation of particle beams with the precision required to tune, operate, and improve the machine. In the first part, the basic mechanisms of information transfer from the beam particles to the detector are described in order to derive suitable performance characteristics for the beam properties. However, depending on the type of accelerator, for the same parameter, the working principle of a monitor may strongly differ, and related to it also the requirements for accuracy. Therefore, in the second part, selected types of accelerators are described in order to illustrate specific diagnostics needs which must be taken into account before designing a related instrument.
Comments: 102 pages, contribution to the CAS - CERN Accelerator School: Beam Instrumentation, 2-15 June 2018, Tuusula, Finland

Introduction to Optics and Lasers for Beam Instrumentation: https://arxiv.org/abs/2007.11272
Stephen Gibson
The versatility of optics enables the design of a wide range of elegant beam instrumentation. Multiple properties of particle beams can be precisely measured by various optical techniques, which include: direct sampling of optical radiation emitted from a charged particle beam; monitoring interactions with an optical probe such as a laserwire; and by electro-optic conversion of the beam signal with high-bandwidth fibre readout. Such methods are typically minimally-invasive and non-destructive, thus permitting diagnostics during accelerator operation without perturbation of the particle beam or risk of damage to the instrument. These proceedings summarise three CAS lectures that introduce the basic principles of optics relevant for instrumentation design, outline the key laser technologies and setups, and review the state-of-the-art in laser-based beam instrumentation.
Comments: 34 pages, contribution to the CAS - CERN Accelerator School: Beam Instrumentation, 2-15 June 2018, Tuusula, Finland

Diagnostics Examples from CTF3: https://arxiv.org/abs/2004.13368

Frank Tecker
After a short introduction of CLIC, the Compact Linear Collider, and its test facility CTF3 (CLIC Test Facility 3), this paper gives an overview and some examples of the diagnostics used at CTF3.
Comments: 10 pages, contribution to the CAS - CERN Accelerator School: Beam Instrumentation, 2-15 June 2018, Tuusula, Finland

Longitudinal Beam Dynamics -- Recap: https://arxiv.org/abs/2004.11908

Frank Tecker
This paper gives a very brief summary of longitudinal beam dynamics for both linear and circular accelerators. After discussing synchronism conditions in linacs, it focuses on particle motion in synchrotrons. It summarizes the equations of motion, discusses phase-space matching during beam transfer, and introduces the Hamiltonian of longitudinal motion.
Comments: 17 pages, contribution to the CAS - CERN Accelerator School: Beam Instrumentation, 2-15 June 2018, Tuusula, Finland. arXiv admin note: substantial text overlap with arXiv:1601.04901

Longitudinal Beam Dynamics: https://arxiv.org/abs/1601.04901
F. Tecker (CERN)
The course gives a summary of longitudinal beam dynamics for both linear and circular accelerators. After discussing different types of acceleration methods and synchronism conditions, it focuses on the particle motion in synchrotrons.
Comments: 21 pages, contribution to the CAS - CERN Accelerator School: Advanced Accelerator Physics Course, Trondheim, Norway, 18-29 Aug 2013

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лошадь, диаграмма, Фейнман

Что-то забавное японцы накрутили...

A Forced Harmonic Oscillator, Interpreted as Diffraction of Light: https://arxiv.org/abs/2004.12675
Toshihiko Hiraiwa, Kouichi Soutome, Hitoshi Tanaka
We investigate a simple forced harmonic oscillator with a natural frequency varying with time. It is shown that the time evolution of such a system can be written in a simplified form with Fresnel integrals, as long as the variation of the natural frequency is sufficiently slow compared to the time period of oscillation. Thanks to such a simple formulation, we found, for the first time, that a forced harmonic oscillator with a slowly-varying natural frequency is essentially equivalent to diffraction of light.
Comments: 4 pages, 3 figures
лошадь, диаграмма, Фейнман

Дешевый портативный МРТ-сканнер для головы

A Portable Brain MRI Scanner for Underserved Settings and Point-Of-Care Imaging: https://arxiv.org/abs/2004.13183

Access to and availability of MRI scanners is typically limited by their cost, siting and infrastructure requirements. This precludes MRI diagnostics, the reference standard for neurological assessment, in patients who cannot be transported to specialized scanner suites. This includes patients who are critically ill and unstable, and patients located in low-resource settings. The scanner design presented here aims to extend the reach of MRI by substantially reducing these limitations. Our goal is to shift the cost-benefit calculation for MRI toward more frequent and varied use, including improved accessibility worldwide and point of care operation. Here, we describe a portable brain MRI scanner using a compact, lightweight permanent magnet, with a built-in readout field gradient. Our low-field (80 mT) Halbach cylinder design of rare-earth permanent magnets results in a 122 kg magnet with minimal stray-field, requiring neither cryogenics nor external power. The built-in magnetic field gradient reduces reliance on high-power gradient drivers, which not only lowers overall system power and cooling requirements, but also reduces acoustic noise. Imperfections in the encoding fields are mitigated with a generalized iterative image reconstruction technique, that uses prior characterization of the field patterns. Our system was validated using T1, T2 and proton density weighted in vivo brain images with a spatial resolution of 2.2 x 1.3 x 6.8 mm3.
Comments: under review at Nature Biomedical Engineering

Апдейт: вот еще предложение по портативному сканеру. но у них много искажений:

In vivo three-dimensional brain and extremity MRI at 50 mT using a permanent magnet Halbach array: https://arxiv.org/abs/2005.02834

Purpose: To design a low-cost, portable permanent magnet-based MRI system capable of obtaining in vivo MR images within a reasonable scan time.
Methods: A discretized Halbach permanent magnet array with a clear bore diameter of 27 cm was designed for operation at 50 mT. Custom built gradient coils, radiofrequency coil, gradient amplifiers and radiofrequency amplifier were integrated and tested on both phantoms and in vivo.
Results: Phantom results showed that the gradient non-linearity in the y- and z-directions was less than 5% over a 15 cm field-of-view and did not need correcting. For the x-direction, it was significantly greater, but could be partially corrected in post-processing. Three dimensional In vivo scans of the brain of a healthy volunteer using a turbo-spin echo sequence were acquired at a spatial resolution of 4x4x4 mm in a time of ~2 mins. T1-weighted and T2-weighted scans showed a good degree of tissue contrast. In addition, in vivo scans of the knee of a healthy volunteer were acquired at a spatial resolution of ~3x2x2 mm within a twelve minutes to show the applicability of the system to extremity imaging.
Conclusion: This work has shown that it is possible to construct a low-field MRI unit with hardware components costing less than 10000 euros, which is able to acquire human images in vivo within a reasonable data acquisition time. The system has a high degree of portability with magnet weight ~75 kg, gradient and RF amplifiers each 15 kg, gradient coils 10 kg and spectrometer 5 kg.
лошадь, диаграмма, Фейнман

Опять бразильцы

From Solar Eclipse of 1919 to the Spectacle of Gravitational Lensing: https://arxiv.org/abs/2001.01549
J. A. S. Lima, R. C. Santos
A century after observing the deflection of light emitted by distant stars during the solar eclipse of 1919, it is interesting to know the concepts emerged from the experiment and the theoretical and observational consequences for modern cosmology and astrophysics. In addition to confirming Einstein's gravitational theory, its greatest legacy was the construction of a new research area to cosmos science dubbed gravitational lensing. The formation and magnification of multiple images (mirages) by the gravitational field of a compact or extended lens are among the most striking phenomena of nature. This article presents a pedagogical view of the first genuine gravitational lens effect, the double quasar QSO 0957 + 561. We also describe the formation of rings, giant arcs, arclets and multiple Supernova images. It is also surprising that the Hubble constant and the amount of dark matter in the Universe can be measured by the same technique. Finally, the lensing of gravitational waves, a possible but still not yet detected effect, is also briefly discussed.
Comments: 22 pages, 20 figures, in Portuguese
лошадь, диаграмма, Фейнман

Маятник Фуко и Алиса в стране переменных действие-угол

Alice and the Foucault Pendulum: the land of action-angle variables: https://arxiv.org/abs/2004.12080
Niciolas Boulanger, Fabien Buisseret
Since the pioneering works of Newton (1643−1727), Mechanics has been constantly reinventing itself: reformulated in particular by Lagrange (1736−1813) then Hamilton (1805−1865), it now offers powerful conceptual and mathematical tools for the exploration of the most complex dynamical systems, essentially via the action-angle variables formulation and more generally through the theory of canonical transformations. We give the reader an overview of these different formulations through the well-known example of Foucault's pendulum, a device created by Foucault (1819−1868) and first installed in the Panthéon (Paris, France) in 1851 to display the Earth's rotation. The apparent simplicity of the Foucault pendulum is indeed an open door to the most contemporary ramifications of Classical Mechanics. We stress that the action-angle variable formalism is not necessary to understand Foucault's pendulum. The latter is simply taken as well-known simple dynamical system used to exemplify modern concepts that are crucial in order to understand more complicated dynamical systems. The Foucault pendulum installed in the collegiate church of Sainte-Waudru (Mons, Belgium) will allow us to numerically estimate the different quantities introduced. A free adaptation of excerpts from "Alice's Adventures in Wonderland" will offer the reader some poetic breaths.
лошадь, диаграмма, Фейнман

Звезда сегодняшнего дня - это, разумеется, пеночка

Она была удивительно близко и долго мне позировала. А все потому, что с увлечением объедала кого-то с листьев. Единственный минус - делала это в тени. Сегодня я опубликую начало фотосессии:

DSC_5488_obr.jpg © qedqed.iMGSRC.RU

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