Showing papers in "Rivista Del Nuovo Cimento in 1995"

The Complementarity of Quantum Observables: Theory and Experiments.

Abstract: Recent advances in experimental quantum physics have made it possible to perform joint measurements of complementary observables of individual quantum objects, like neutrons or photons. Despite its apparently contradictory nature, this statement is in full harmony with the quantum theory, the theory of complementarity [1], being, in fact, anticipated in the notion of coexistence. The concept of complementarity has both probabilistic and operational contents. When these two aspects are clearly distinguished, it becomes evident that probabilistically complementary observables may also be coexistent so that they can be measured together. This is exactly the situation encountered in recent experiments or in proposals for such experiments.

The Avogadro constant

Abstract: The ubiquitous character ofN A has been described by summarizing the results obtained in different periods with different methods and by illustrating in more detail the X-ray crystal-density method. A careful analysis of the quantities involved demonstrates that the search for systematic errors is endless. At present, metrological laboratories are engaged in reducing the relative uncertainty from the 10−7 to the 10−8 level or better. If this could be achieved, a new definitiona la Maxwell of the mass unit, and the relevant realization, would be feasible. However, the main justification, to continue devoting human and financial resources, lies within a wider framework. The loop starts with the observation that fundamental constants were the foundations on which Science rested when solid-state physicists, in the forties and fifties, developed the transistor, a significant step in computer technology. The subsequent increasing demand from the micro-electronics industry led to the production of near-perfect silicon monocrystals which were instrumental in the realization of X-ray interferometry; this new kind of interferometry, in its turn, triggered substantial improvements which led to a more accurate value ofN A . The loop closes with the observation thatN A , as a result of the continuous interaction between Physics and Technology, has contributed to strengthening the edifice of the fundamental constants.

Synchrotron light and free-electron lasers

Abstract: Keywords: PHOTOELECTRON MICROSCOPY ; PHOTOEMISSION ; SPECTROMICROSCOPY ; RADIATION ; SPECTRA Note: Sincrotrone,trieste,italy. vanderbilt univ,dept phys & astron,nashville,tn. Margaritondo, g, ecole polytech fed lausanne,inst phys appl,ch-1015 lausanne,switzerland.ISI Document Delivery No.: QY304 Reference LSE-ARTICLE-1995-029View record in Web of Science Record created on 2006-10-03, modified on 2016-08-08

Advanced imaging techniques: A new deal for neutron physics

Abstract: Among non-destructive evaluations and methodologies—the important set of analyses which preserve the integrity of the tested object—neutron imaging techniques, and neutron computerized tomography in particular, represent powerful tools. Although they have been considered more an amusement for scientists rather than an effective tool for engineers until few years ago, it can be stated that they can now provide valuable quantitative results in many circumstances of interest, being the only available choice in some specific cases. This wider interest and the attempt to give neutron imaging a certain prominence reflect themselves in the birth of an international group of people involved in the field of neutron research; the so-called ENRWG (European Neutron Radiography Working Group). Connected to a general interest and a diffuse curiosity in the fascinating interactive world of INTERNET there is also the possibility, since last year, to get information about neutron radiography state of the art and current projects from a free-access WWW site. As a consequence of these fervent activities, a new deal in studies of advanced materials, sources, detectors and algorithms is now growing to promote and to develop the capabilities of neutron imaging techniques after a long period during which the interest in neutron physics and in their applications was limited to selected specialists involved in the nuclear-energy production. The results of this effort will not be limited to improved technological processes, but will include an improved knowledge in relevant fields of nuclear and material science.