Search results for "Ilw"

Test of relativistic time dilation with fast optical atomic clocks at different velocities

2007

Time dilation is one of the most fascinating aspects of special relativity as it abolishes the notion of absolute time. It was first observed experimentally by Ives and Stilwell in 1938 using the Doppler effect. Here we report on a method, based on fast optical atomic clocks with large, but different Lorentz boosts, that tests relativistic time dilation with unprecedented precision. The approach combines ion storage and cooling with optical frequency counting using a frequency comb. 7Li+ ions are prepared at 6.4% and 3.0% of the speed of light in a storage ring, and their time is read with an accuracy of 2×10−10 using laser saturation spectroscopy. The comparison of the Doppler shifts yield…

Test of Time Dilation Using StoredLi+Ions as Clocks at Relativistic Speed

2014

We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt. A Λ-type three-level system within the hyperfine structure of the 7Li+3S1 →3P2 line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler shifted frequencies required for resonance are measured with an accuracy of <4×10(-9) using optical-optical double resonance spectroscopy. This allows us to verify the special relativity relation between the time dilation factor γ and the velocity β, γ√1-β2=1 to within ±2.3×10(-9) at this velocity. The result, which is singled …

Test of special relativity in an ion storage ring

1996

An accurate measurement of the Doppler effect in collinear laser spectroscopy has been performed at the TSR storage ring with electron cooled7Li+ ions atΒ=0.064. This experiment is a sensitive test of theγ=(1−Β2)−1/2 factor(Β=v/c) in the special theory of relativity. The Doppler shifted frequencies of the moving7Li+ ions are compared with calibrated molecular lines at rest. The frequencies at rest for the7Li+ ions are known from independent measurements. The Doppler shifted frequencies in the collinear experiment have been measured with a precision ofδv/v=6×10−9, mainly limited by the signal width of the resonance. A corresponding upper limit of 8×10−7 is deduced for any deviation of the ti…

A new type of railway monoblock sleeper

2012

A railway sleeper is the structural element which transversally connects the two rails by means of fastening components, thus ensuring its gauge. Its additional function is to firmly secure the track to the ballast and to distribute the loads transferred from railway carriages to the ballast. One of the most important parameters in the characterisation of performances given by railway sleepers is represented by their lateral resistance to the sliding: the higher its value increases, the better the track stability becomes, thus reducing the frequency of maintenance interventions necessary to keep the superstructure efficient. This article focuses on the performance profile of an innovative r…

A MARKOVIAN MODEL AS A TOOL FOR OPTIMISATION OF MAINTENANCE INTERVENTIONS ON RAILWAYS LINES

2008

This paper is designed to develop a procedure which defines a planning criterion for railway superstructure maintenance by means of Markov decision processes. This methodology allows to formulate a specific policy  which carries out the best configuration of budget allocation (min. Ф), and at the same time to guarantee the highest efficiency level in the railway superstructure. Thanks to the dynamic programming technique applied to decision processes, the report has examined the possibility of establishing the best management policy in order to maintain adequate safety levels of implementation and quality speed levels, in the presence of budget constraints, thus optimizing the available re…

French railway history in geo-historical perspectives, infrastructure, demographic dynamics and territorial change

2014

International audience

Les traces de la vitesse entre réseau et territoire : approche géohistorique de la croissance du réseau ferroviaire français

2016

The interaction between space and network are frequently questioned in the academic literature, by asking the economical and demographical impacts of a new infrastructure, often studied at the scale of a project. This work aims to investigate the components of the interaction in both large spatial and temporal scales. The hypothesis is that the temporal depth and the national scale could bring new explanations. This work is based on the collect, the exploitation and the analysis of the large spatio-temporal database FRANcE (French Railway Network). It identifies all sections of the network since the 19th century and the population census. This database also contains the traces of the speed,…

Nuove stazioni, periferie e città

2016

L’infrastruttura contemporanea amplia e fa slittare il proprio campo semantico, trasformandosi definitivamente da artefatto tecnico di carattere titanico ed epico ad elemento riparatore dei tessuti urbani, flessibile, trasformabile. In questo quadro in mutazione, numerose esperienze negli ultimi trent’anni hanno affermato in Europa occidentale il ruolo dei grandi progetti ferroviari come vettori di trasformazione urbana. A quindici anni dall’avvio della prima stagione di concorsi internazionali banditi per le nuove stazioni dell’Alta Velocità in Italia, è possibile un bilancio volto non solo al semplice confronto dei risultati direttamente pertinenti la realizzazione e l’esercizio dell’oper…

Mechanical characterisation and 3D fractional viscoelastic modelling of railway sub-ballast rubberised asphalt

SAFETY PROBLEMS AND GLOBAL COMFORT IN RAILWAYS OPERATIONAL MANAGMENT

2008

In the planning process of a railway intervention and in its operational management, it needs to analyse carefully the relations between the different classes of variables constituting the complex system “vehicle-infrastructure-environment” to find the most suitable actions in optimisation the travelling comfort and safety, with respect for the ecosystem compatibilities. The problem can be tackled, in a systematic way, according to set theory and vector analysis, in a hyperspace Âd of d-dimension up to determining a characteristic global comfort vector that can be combined with each alternatives of intervention in the transport network examined. From this point of view, after the proper ach…