Combining fluorescence and transmitted light sources for microscopy is an invaluable method in cellular neuroscience to probe the molecular and cellular mechanisms of cells. This approach enables the targeted recording from fluorescent reporter protein expressing neurons or glial cells in brain slices and fluorescence-assisted electrophysiological recordings from subcellular structures. However, the existing tools to mix multiple light sources in one-photon microscopy are limited. Here, we present the development of several microcontroller devices that provide temporal and intensity control of light emitting diodes (LEDs) for computer controlled microscopy illumination. We interfaced one microcontroller with μManager for rapid and dynamic overlay of transmitted and fluorescent images. Moreover, on the basis of this illumination system we implemented an electronic circuit to combine two pulsed LED light sources for fast (up to 1 kHz) ratiometric calcium (Ca2+) imaging. This microcontroller enabled the calibration of intracellular Ca2+ concentration and furthermore the combination of Ca2+ imaging with optogenetic activation. The devices are based on affordable components and open-source hardware and software. Integration into existing bright-field microscope systems will take ∼1 day. The microcontroller based LED imaging substantially advances conventional illumination methods by limiting light exposure and adding versatility and speed.
Simulations have been performed of the radial transport of antiprotons in positron plasmas under ambient conditions typical of those used in antihydrogen formation experiments in Penning traps. The simulations were performed using classical trajectories of both antiprotons and surrounding positrons with randomized initial conditions. In addition, friction and fluctuation forces on the antiproton due to interaction with the positron plasma were included. This gives rise to both axial and radial diffusion of the antiprotons at a rate given by the magnetic field, the positron temperature and the plasma density, and the parameter range explored includes at least two values of each. As the antiprotons travel through the positron plasma they undergo repeated cycles of antihydrogen formation and reionization. We find that when these effects are added to the simulations the properties of the radial diffusion alter dramatically, even changing from normal to anomalous diffusion. We attribute this to the azimuthal drift of the antiprotons in the crossed magnetic (from the trap) and electric fields (from the space charge of the plasma). When the antiprotons are neutralised through antihydrogen formation this drift is temporarily interrupted, and the antiproton (carrying a positron) continues in the tangential direction. On average this motion will give an increase of the radial position of the antiproton, relative the trap axis. At low positron plasma temperatures, repeated cycles of antihydrogen formation and destruction are the dominant source of radial (cross magnetic field) transport. On time scales of a few milliseconds (depending on plasma parameters) the antiprotons will reach the edge of the cylindrical plasma, where the radial transport will cease, and thus the antiprotons will accumulate there.
Il arrive que les occasions d'apprentissage et d'acquisition des compétences et des aptitudes soient tiées aux opportunités professionnelles et ainsi, indirectement, au développement de l'économie. L auteur illustre, avec cinq scénarios, comment l'apprentissage peut être conditionné par des choix macro‐économiques et macro‐sociaux. Opportunities for learning and the acquisition of competences or skills happen to be linked to work opportunities and thence indirectly to the development of the economy. The author sketches five scenarios indicating how learning may be conditioned by macroeconomic and macro‐social choices.
The GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN has been proposed to measure the gravitational acceleration of the ultracold antihydrogen atoms. This experiment produces antihydrogen ions through interactions between antiprotons and positronium atoms. Then, antihydrogen atoms are produced for the free-fall experiment after the photo-detachment of an excess positron from the cold antihydrogen ions. The energy of the antiproton beam before the positronium target chamber will be in the range of 1–10 keV. The cross-section for the reaction between the antiprotons and positroniums depends mainly on the energy of the antiprotons. Hence, to maximize the productivity of antihydrogen ions, a sufficient number of antiprotons should be provided with well-controlled energy. In this regard, an antiproton trap is considered to accumulate and slow down antiproton beams, and cool them utilizing the electron cooling technique. This trap is designed based on the Penning-Malmberg trap, which consists of a superconducting solenoid magnet and a series of ring electrodes including high-voltage electrodes to trap antiprotons. In addition, a set of extraction electrodes and optics for beam transport are used. Each electrode has been designed and optimized using the WARP PIC simulations. In this study, the design and simulation results of each trap component are presented.
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