David Brewster's and William Herschel's experiments on inflection that delivered the coup de gr{\^a}ce to Thomas Young's ether distribution hypothesis

In his Theory of Light and Colours, presented to the Royal Society in November 1801, Thomas Young defended a mechanical explanation of the coloured fringes observed outside of the shadow of an opaque object-the so-called 'colours by inflection'-that was based on the hypothesis of an ethereal density gradient surrounding all material bodies. However, two years later, he publicly rejected that hypothesis, without giving much detail on his reasons. Now, although Geoffrey Cantor demonstrated the crucial role of mechanical and astronomical arguments in explaining the withdrawal of this fundamental hypothesis long ago, the purpose of this article is to draw deeper attention on a set of experiments performed by David Brewster on the inflection of light, described in a letter he addressed to the Royal Society in January 1802, but which kept retained in the hands of William Herschel and never reached its original destination. For the hypothesis that will be evaluated here is that these unpublished experiments of Brewster's were eventually known to Young through the mediation of William Herschel, and eventually played a significant role in his rejection of his own ether distribution hypothesis too.Comment: Accept{\'e} en octobre 2023 pour publication dans Annals of Science, revue publi{\'e}e par Taylor and Franci

Faire des liens - mais lesquels ? Pour une théorie pratique de l'analogie

International audienceLe propre d'une approche transdisciplinaire, en recherche comme en enseignement, consiste à faire des liens. Cette injonction, l'expérience de la Licence Sciences et Humanités de l'université d'Aix-Marseille a montré qu'elle était parfois problématique, et l'on pourrait résumer son enjeu par la double contrainte suivante : si l'exercice consiste à faire des liens originaux et audacieux entre disciplines, il s'agit aussi de faire des liens qui soient pertinents. Comment peut-on évaluer la pertinence de certains liens, et comment exclure ou limiter les liens non pertinents, arbitraires, superficiels ? Ce problème implique la nécessité d'une enquête méthodologique portant sur l'analogie. Nous traduisons en effet techniquement "lien" par le concept de théorie de la connaissance « analogie », dont nous analyserons deux formes historiques dans l'histoire des sciences. Par analogie, nous n'entendons pas ici la similarité, ou l'égalité de rapport qui définit l'acception mathématique du concept, mais l'opération cognitive qui met en relation des phénomènes en vertu d'une ressemblance quelconque, dans le but d’éclairer le phénomène le moins connu depuis les savoirs possédés concernant le mieux connu

Agile low phase noise radio-frequency sine wave generator applied to experiments on ultracold atoms

We report on the frequency performance of a low cost (~500$) radio-frequency sine wave generator, using direct digital synthesis (DDS) and a field-programmable gate array (FPGA). The output frequency of the device may be changed dynamically to any arbitrary value ranging from DC to 10 MHz without any phase slip. Sampling effects are substantially reduced by a high sample rate, up to 1 MHz, and by a large memory length, more than 2.10^5 samples. By using a low noise external oscillator to clock the DDS, we demonstrate a phase noise as low as that of the master clock, that is at the level of -113 dB.rad^2/Hz at 1 Hz from the carrier for an output frequency of 3.75 MHz. The device is successfully used to confine an ultracold atomic cloud of rubidium 87 in a RF-based trap, and there is no extra heating from the RF source.Comment: 10 pages, 6 figure

Les Secrets du Monde de Johannes Kepler. Où astrologie, métaphysique et histoire enrichissent l'enseignement de l'astronomie

International audienceCeci n'est pas un article d'histoire ou de philosophie des sciences. Ceci n'est pas non plus un article de didactique, de physique, ou d'astronomie, non plus qu'une tentative de réhabilitation de l'astrologie. Ceci est un peu de tout cela. Mais ceci est surtout un récit. Le récit d'un cours dans la licence Sciences et Humanités, de sa construction et de la quantité de choses que j'ai apprises-y compris dans mon domaine (la physique)-le jour où j'ai accepté que je ne savais pas grand-chose de ma propre discipline. Ce format paraîtra peut-être surprenant, et je me suis évidemment interrogé sur l'intérêt de soumettre un tel texte plutôt qu'un compte-rendu plus formel et synthétique. Ainsi me suis-je demandé si j'avais déjà lu ce genre de texte ailleurs, et s'il m'avait paru pertinent. Alors m'est immédiatement revenue en tête la préface du Mysterium Cosmographicum, premier ouvrage publié par Johannes Kepler 1 : Mon dessein, Lecteur, est de démontrer dans ce petit ouvrage que le Créateur Très Bon et Très Grand s'est référé pour la création de ce monde mobile et la disposition des cieux à ces cinq corps réguliers qui, depuis Pythagore et Platon jusqu'à nos jours, ont acquis une si grande célébrité 2 , et qu'il a ordonné en fonction de leur nature le nombre des cieux, leur proportion et le rapport de leur mouvement. Mais avant que je ne te permette d'en venir au sujet lui-même, je voudrais te dire, tant sur l'occasion de ce petit livre que sur la raison de mon entreprise, certaines choses qui, à mon avis, te permettront de mieux comprendre et de mieux me connaître. Comme l'aurait certainement fait le maître, j'ai interprété cela comme un signe, et me suis engagé sans plus hésiter dans la rédaction du texte que vous trouverez avez entre les mains. Dans ce récit, vous me verrez enfoncer beaucoup de portes ouvertes. Si vous venez des sciences humaines, vous saurez alors que ces portes nous semblent bien fermées à nous physiciens, et qu'il nous a fallu bien du temps et des efforts pour en trouver la poignée. Si vous venez des sciences de la matière, voyez combien de portes ont été ouvertes par nos collègues des autres disciplines que nous n'avons qu'à franchir. Au-delà d'informer sur les idées et travaux de Kepler et ce qu'ils peuvent apporter aux étudiants, ce texte a donc pour but de faciliter le dialogue entre ses lecteurs, en soulignant régulièrement les motivations, les apports, mais aussi les erreurs et les a priori qui ont donné leur forme actuelle à ce cours et qui furent propres au spécialiste des sciences physiques que je suis

Regulating TRAIL Receptor-Induced Cell Death at the Membrane: A Deadly Discussion

The use of TRAIL/APO2L and monoclonal antibodies targeting TRAIL receptors for cancer therapy holds great promise, due to their ability to restore cancer cell sensitivity to apoptosis in association with conventional chemotherapeutic drugs in a large variety of tumors. TRAIL-induced cell death is tightly regulated right from the membrane and at the DISC (Death-Inducing Signaling Complex) level. The following patent and literature review aims to present and highlight recent findings of the deadly discussion that determines tumor cell fate upon TRAIL engagement

Historical synthesis supporting Duhem's demonstration of the impossibility of the `experimentum crucis' of comparison of the speed of light in air and water

In 1850, Foucault was the first to compare experimentally the velocity of light in air to its velocity in water. And as the wave and projectile theories competing at the time predicted inverse results to such a measurement, Foucault ''declared the emission system incompatible with the reality of the facts''. Yet, in his Physical Theory, Duhem uses this very example to illustrate his epistemological demonstration of the impossibility of the 'experimentum crucis' in physics. Then, the ambition of the present article is to augment Duhem's demonstration with historical evidence relating precisely to the question of the speed of light in water. We will review the four major opinions on the nature of light developed between 1637 and 1801; all leading to theories concluding that the ratio of sines is constant and equal to the ratio of the velocities in the two media, but all being defended by at least two authors concluding to inverse ratios of those velocities -- and thus to opposite predictions on the result of an experiment such as Foucault's. The convergence of historical evidence will then confirm that the nature of light, considered in isolation, is in no way constrained by the measurement of its speed in water.Comment: in French language, Article accept{\'e} pour publication dans la revue Archives Internationales d'Histoire des Sciences, 2023, {\'e}dit{\'e}e par Brepol

A ring trap for ultracold atoms

We propose a new kind of toroidal trap, designed for ultracold atoms. It relies on a combination of a magnetic trap for rf-dressed atoms, which creates a bubble-like trap, and a standing wave of light. This new trap is well suited for investigating questions of low dimensionality in a ring potential. We study the trap characteristics for a set of experimentally accessible parameters. A loading procedure from a conventional magnetic trap is also proposed. The flexible nature of this new ring trap, including an adjustable radius and adjustable transverse oscillation frequencies, will allow the study of superfluidity in variable geometries and dimensionalities.Comment: 4 figures, 10 pages ; the order of the sections has been changed ; to appear in Phys. Rev.

Noise characterization of an Optical Frequency Comb using Offline Cross-Correlation

Using an offline cross-correlation technique, we have analyzed the noise behavior of a new type of optical frequency comb (OFC), which is carrier envelope offset (CEO) free by configuration, due to difference frequency generation. In order to evaluate the instrument's ultimate noise floor, the phase and amplitude noise of a stabilized OFC are measured simultaneously using two analog-to-digital converters. Carrier recovery and phase detection are done by post-processing, eliminating the need for external phase-locked loops and complex calibration techniques. In order to adapt the measurement noise floor and the number of averages used in cross correlation, an adaptive frequency resolution for noise measurement is applied. Phase noise results are in excellent agreement with measurements of the fluctuations of the repetition frequency of the OFC obtained from optical signal

Coherent internal state transfer by three-photon STIRAP-like scheme for many-atom samples

A STIRAP-like scheme is proposed to exploit a three-photon resonance taking place in alkaline-earth-metal ions. This scheme is designed for state transfer between the two fine structure components of the metastable D-state which are two excited states that can serve as optical or THz qu-bit. The advantage of a coherent three-photon process compared to two-photon STIRAP lies in the possibility of exact cancellation of the first order Doppler shift which opens the way for an application to a sample composed of many ions. The transfer efficiency and its dependence with experimental parameters are analyzed by numerical simulations. This efficiency is shown to reach a fidelity as high as $(1-8.10^{-5})$ with realistic parameters. The scheme is also extended to the synthesis of a linear combination of three stable or metastable states.Comment: Journal of Physics B: Atomic, Molecular and Optical Physics (2013) a paraitr

Trapping and cooling of rf-dressed atoms in a quadrupole magnetic field

6 pages, 6 figures; to appear in J. Phys. BInternational audienceWe observe the spontaneous evaporation of atoms confined in a bubble-like rf-dressed trap (Zobay and Garraway, 2001). The atoms are confined in a quadrupole magnetic trap and are dressed by a linearly polarized rf field. The evaporation is related to the presence of holes in the trap, at the positions where the rf coupling vanishes, due to its vectorial character. The final temperature results from a competition between residual heating and evaporation efficiency, which is controlled via the height of the holes with respect to the bottom of the trap. The experimental data are modeled by a Monte-Carlo simulation predicting a small increase in phase space density limited by the heating rate. This increase was within the phase space density determination uncertainty of the experiment