Quanta: The Originality of Einstein's Approach to Relativity?

We suggest that not only quanta may have played a role in Einstein's ideas on relativity, but that they themselves may be related to the dynamical and relativistic behaviour of the electromagnetic field exhibited in a Poincar\'e's 1900 paper, in particular to the identical transformation law of energy and frequency for bounded plane waves

Einstein et Besso : de Zürich à Milan

International audienceThe 1896-1901 Milanese period is a key one to understand Einstein’s training background. When he was a student at the ETH in Zürich (the Swiss Federal Polytechnic in Zürich) from 1896 to 1900, he would make regular trips back to Milan to stay with his family who was involved in the development of the electricity industry in northern Italy. Between 1899 and 1901, he would meet his faithful friend and collaborator, Michele Besso in Milan on a regular basis. Given their relationship, the 1899-1901 Milanese period therefore foreshadowed the Bern period. In order to specify the circumstances under which Einstein and Besso got the chance to meet, we will show that their respective families did have interconnected social networks, especially through the electricity sector and the polytechnic engineering Universities of Zürich and Milan. The branch of the Cantoni family, on Michele’s mother’s side, rather ignored by now, played a crucial role: with Vittorio Cantoni, a renowned electrical engineer who had not been previously identified as being Michele’s uncle, and Giuseppe Jung, professor at the Milan Politecnico. We will also show that when staying in Milan, Einstein, who lived in a well-known Milanese palace in the heart of the city, worked in the nearby rich library of the Istituto Lombardo, Accademia di Scienze e Lettere in Brera. The linkage between the scientific observations which can be found in Einstein’s correspondence and this library collection sheds new light on his scientific work, in particular on his original thesis.La période milanaise 1896-1901 est une période clé pour comprendre les années de formation d'Albert Einstein. Alors étudiant à l'ETH de Zurich entre 1896 et 1900, il rejoint régulièrement sa famille, installée à Milan, et impliquée de longue date dans le développement de l'électricité en l'Italie du nord. Entre 1899 et 1901, il y retrouve son ami et collaborateur, Michele Besso, qu'il avait connu à Zurich. Du point de vue de la relation Einstein-Besso, la période milanaise 1899-1901 préfigure celle de Berne à partir de 1904, où les deux amis se retrouvent au Bureau des Brevets. Afin de préciser le cadre de leur rencontre, nous mettrons en évidence les liens de leurs familles respectives avec le milieu de l'électricité et des écoles polytechniques de Zurich, Milan. La branche maternelle de la famille de Michele, relativement ignorée jusqu'à présent, tient un rôle important, avec Vittorio Cantoni, ingénieur en chef de la première ligne de transport de courant alternatif en Italie entre Tivoli et Rome, qui n'avait pas été identifié auparavant comme étant un oncle de Michele, et Giuseppe Jung, professeur de mathématiques au Politecnico de Milan, avec lequel Einstein est resté en contact plusieurs années. Nous montrerons aussi qu'Einstein, qui habite un célèbre palais milanais au coeur de la ville, travaille à la riche bibliothèque scientifique de l'Istituto Lombardo, Accademia di Scienze e Lettere située au palais Brera, à 500 mètres de son domicile. La mise en rapport des remarques scientifiques qui apparaissent dans la correspondance d'Albert Einstein avec le fonds de cette bibliothèque apporte un éclairage nouveau sur son travail, en particulier sur sa thèse originale

Development and assessment of tools for quantitative dynamic contrast enhanced MRI of bone metastases from breast and prostate cancer

The microenvironment of solid human tumors is characterized by heterogeneity in oxygenation and by proliferation of a network of blood vessels that provides oxygen and nutrients and removes waste products. The capability of a tumor to metastasize is linked to the well known hyper permeability of tumor vessels; in fact angiogenic primary tumors possess a large number of micro-vessels through which the metastasizing cells are shed into the blood stream. Pioneering studies performed by Folkman in 1971 proposed an insightful anticancer therapy by starvation of blood supply, Folkman's intuition that tumor growth and metastasis strictly depend on angiogenesis led to the idea that blocking tumor nourishment could be one of the ways to avoid its spread. Many imaging strategies have been used to determine angiogenesis in vivo, among them Dynamic Contrast Enhanced MRI (DCE-MRI) which provides a powerful tool for the rapid evaluation of the acute pharmacodynamic effect of the most recent agents in clinical trials, most notably in the case of mechanisms that affect tumor perfusion. One of the attractives of dynamic post contrast imaging is the insight it offers into the distribution kinetics of contrast agent in the tissue. These quantities are generally derived from simple models of the tissue as a compartmentalized system (usually a plasma-interstitial two-compartments model is used), using a kinetic analysis originally developed for use with nuclear medicine tracers. In this study a three parameters model has been used in order to describe the transport of tracer in the tissues. The first one takes into account the plasma volume in the voxel or in the region of interest being examined, the second is related to the amount of tracer that enters the EES and the last one determines the washout rate from EES back into the blood plasma. An artery input function (AIF), namely the concentration of contrast in the plasma, is provided as well. In order to obtain these parameters it is necessary to perform the fit of the chosen model on the concentration-curves vs time. It is possible to correlate the contrast agent concentration with the difference of relaxation rate (the inverse of longitudinal relaxation time); this way the concentration-curves can be achieved by means of T1-weighted images. In this work, an acquisition protocol has been optimized in order to provide the images from which extracting the data related to the tumor perfusion. Post processing tools, which carry out the fitting, the smoothing, and, the registration, have been developed and tested, as well. These tools can provide the oncologysts and radiologists a way to perform reproducible and quantitative estimation of the tumor perfusion in anti-angiogenic therapy

Henri Poincaré : du « principe de mouvement relatif » au « principe de relativité » en passant par le « principe de réaction » et son rapport à la théorie de Lorentz

Le « principe de relativité » apparaît dans sa forme moderne en 1905, dans les travaux de Henri Poincaré « Sur la dynamique de l’électron ». Mais l’élévation du principe de relativité (galiléen) de la mécanique (newtonienne) au rang de principe général gouvernant toute la physique a été l’objet d’une gestation complexe chez Poincaré. Nous en retraçons les principales étapes en commençant par son cours de physique à la Sorbonne en 1889, où il généralise les conclusions de Fresnel de 1818 sur la réfraction dans l’expérience du prisme d’Arago (le « principe de mouvement relatif » étendu à l’optique). Nous nous intéressons ensuite à ses articles scientifiques dans la revue l’Éclairage électrique en 1895, où il confronte la théorie de Lorentz au principe de réaction newtonien qui s’applique à la matière seule (son « objection » à la théorie). Poincaré soulève à cette occasion la « connexion » de ce principe avec le « principe de mouvement relatif ». Pour mieux comprendre ces enjeux nouveaux, nous revenons en détail sur l’article fondamental de Poincaré « La théorie de Lorentz et le principe de réaction », à l’occasion du Jubilé pour Lorentz de décembre 1900, où Poincaré précise à quelles conditions ces principes s’étendent à l’électrodynamique. Pour conclure, nous verrons comment, en 1905, le « principe de mouvement relatif » devient « principe de relativité » en lien avec la « cohérence parfaite » de la théorie de Lorentz. Notre article est le premier, à notre connaissance, à donner une perspective d’ensemble aux travaux de Poincaré de 1889 à 1900 mentionnés ci-dessus et à la logique qui les relie.The principle of relativity first appeared in its modern form in 1905 in the works of Henri Poincaré “On the dynamics of the electron”. However, establishing the (Galilean) principle of relativity of (Newtonian) mechanics as a general principle of physics had a complex gestation in Poincaré’s works. We discuss his physics course at the Sorbonne in 1889 in which he generalized Fresnel’s conclusions of 1818 on refraction in Arago’s prism experiment (the “principle of relative motion” extended to optics). Then we discuss his scientific articles in the journal Éclairage électrique in 1895 in which he confronted Lorentz’s theory with the Newtonian principle of reaction that applies to matter alone (his “objection” to the theory). Poincaré emphasizes herein the “connection” of this principle with the principle of relative motion. In order to better understand this issue, we return in detail to Poincaré’s fundamental article “The theory of Lorentz and the principle of reaction” on the occasion of the December 1900 Jubilee celebration of Lorentz’s defence of his doctoral thesis in which he specifies the conditions required to extend these principles to electrodynamics. In conclusion, we will see how in 1905, the principle of relative motion becomes the “postulate of relativity” in connection with the “perfect coherence” of Lorentz’s theory. To our knowledge our article is the first to give an overall perspective of the works of Poincaré from 1889 to 1900 as mentioned above and to the logic that connects them