Space | EPFL Graph Search

Space is a three-dimensional continuum containing positions and directions. In classical physics, physical space is often conceived in three linear dimensions. Modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework. Debates concerning the nature, essence and the mode of existence of space date back to antiquity; namely, to treatises like the Timaeus of Plato, or Socrates in his reflections on what the Greeks called khôra (i.e. "space"), or in the Physics of Aristotle (Book IV, Delta) in the definition of topos (i.e. place), or in the later "geometrical conception of place" as "space qua extension" in the Discourse on Place (Qawl fi al-Makan) of the 11

Analysis of Femtosecond Electron Bunches at the SwissFEL Injector Test Facility

Bennie Smit

The SwissFEL (Swiss Free Electron Laser) is a free electron laser which is being built at the Paul Scherrer Institute. The SwissFEL will be a user facility to study processes on unexplored scales of space and time. In order to achieve these aims, X-ray pulses on the order of femtoseconds must be generated. For such short X-ray pulses, the electron bunch length must be comparable to the final X-ray pulse length. In order to achieve such a short electron bunch length, it must be monitored at every compression stage. This work proposes two novel methods to measure such electron bunches, namely a novel spectral method that analyses the frequency content of electron bunches that becomes easier with shorter bunch length and a transverse deflecting cavity method which can conceptually measure a zero bunch length. Because the SwissFEL was not built at the time of the PhD, all experiments were performed at the SwissFEL Injector Test Facility (SITF). The SITF is a 200 MeV test bed linear electron accelerator. Theoretically the bunch length is limited due to the uncorrelated energy spread and the higher order components of the bunch compressor. However, due to the limited electron energy in combination with the short electron bunches, space charge effects dominate the beam in the transverse phase space as well as in the longitudinal phase space. A transverse deflecting cavity (TDC) measurement was used to measure a reference bunch length to which the spectral fluctuations could be correlated. In a TDC the electric fields are oriented perpendicular to the beam direction and streaks the head and tail in opposite directions onto a screen. In a conventional TDC measurement, the projected beam size onto the temporal axis is the current profile, provided that the intrinsic beam size is small. However, in the SITF the intrinsic beam size was large due to the aforementioned space charge effects. This led to the development of a novel bunch length analysis method in a space charge dominated beam. In the proposed analysis method, a dispersive section in combination with a TDC was used to visualise the longitudinal phase space. The longitudinal phase space was sliced in the momentum domain to reveal the difference between the intrinsic and the streaked beam in a momentum slice. The bunch length could be extracted by recording the times for all slices. Both the simulations and experiments suggest the method enables the measurement of bunch length in a space charge dominated beam in which the transverse intrinsic beam size is large. The measured minimal bunch length from simulations and experiments are of the same order, 19.5 fs to 24.5 fs, respectively. Since the TDC at PSI has a specified resolution of 20 fs at 200 pC, this method may be used to reduce the resolution. The spectral content of femtosecond electron bunches contains electron bunch length information. As an electron beam collides with an optical transition radiation (OTR) foil, radiation is emitted. The radiation is collected by means of a mirror setup into an optical fibre and into an optical spectrometer. The spectral range of the spectrometer is 316 THz (950 nm) to 1364 THz (220 nm). From OTR theory a flat OTR spectrum was expected and measured. As the electron bunch length was reduced below 70 fs, periodic fluctuations started to appear on the spectra. These fluctuations broaden with decreasing bunch length and show a good agreement with the bunch length measured with the TDC.

EPFL2015

Images des microcosmes flottants

Olivier Nicolas Meystre

This research focuses on the premise that depiction is quintessential to the conception of an architectural project. The representation also provides insights regarding how the architects design the architecture. This thesis is intended towards understanding new forms and paradigms of design mediation that have emerged over the last two decades in Japan. It unravels and highlights the historical, theoretical aspects and analyses the evolution, convergence and major trends in the field of architectural representation. Based on bibliographical sources and exclusive, unpublished interviews with the prominent Japanese architects of the period under consideration, this work presents six cross-functional themes with the objective to identify and examine the critical tools that could be used in the conception and representation of the contemporary Japanese architecture. The understanding of the underlying techniques reveal a very hybridised landscape of digital and analog tools with a paradoxical objective of imparting a manual effect to the entire expression. The treatment of light in the images of the project is characterised by overexposure and dispersion that adds an elusory, unseizable dimension to the objects and spatial limits. In a similar fashion, the graphical limits, are either diminished or diluted giving an impression of a space with evolving outlines. The pseudo-naive expression of multiple images, achieved by the profusion of familiar objects, obliterates the orthodox hierarchy among the architectural elements and opens up the possibility of evoking and imagining tiny, soothing universes in an architecture which is otherwise radical to the beholder. The point of view used in images transcend the Euclidean realism, producing an imagery that seems to float in free space. Finally, the genealogy of relationship between masters and students permits the tracing of the lines of influence, how the craftsmanship changed hands and percolated down the professional world. The specificities in the Japanese representation are a testimony to the complex approach of the architects towards an architectural project, where all the attributes of space are questioned and redefined but still the undercurrent of tradition continues to have a pivotal influence.

EPFL2015

Habiter la ville ouverte

Didier Challand

Between 2002 and 2004 Martin Steinmann gave a close insight to the urban villa, a building type well-known a century ago in our cities and recently brought to the foreground as a major architectural issue in the German speaking part of Switzerland. Through an article1, an exhibition2 and his architectural design teaching at the EPFL3 he introduced various interpretations of a pre-existing housing type's new identity, which this dissertation suggests to further investigate. In the spirit of a monographic contribution, we analyze the urban villa as a multi-unit housing type through its key historical moments, from the rented houses of Lausanne built around 1900 (Part I – Première actualité) until contemporary outstanding realisations (Part III – Nouvelle actualité). Through a typo-morphologic analysis and a sensitive reading of space, major issues such as the urban villa's placement among its surroundings, the subtle amalgamation of individuality and collectivity, as well as the insertion of a constructed nature into the urban cityscape, arise. In the spirit of a polemic contribution, we consider the ville ouverte issue as an intermediate condition of groups of villas or small blocks enhancing all four orientations (Part II – Habiter la ville ouverte, cinq essais). In order to describe the spatial mechanisms of their so-called urbanity, we analyse some coherent groups of urban forms, which belong to the hygienist era running from 1850 until 1930. Those correspond to various programmatic motivations and socio-economical conditions, whose architectural effects we highlight. The contribution of this research is particularly important in view of contemporary residential areas' densification, for it is a densification willingly crystallizing into open urban forms composed of small multi-unit blocks. As neat as they may be, those buildings have not much to offer other than merely "a cute view", "the freshening greenery around the house" or "that big balcony". In his article in 2002 Steinmann proposed a more complex reading of this open urban forms' architecture, which he based on "the sensitive experiences' density". Through the writer's references, a tendency to interpret urban space as a fluid sequence is made apparent. In the Introduction, we thus describe this affinity as "nemourian imaginary"4. Consequently, this preference invites us to speculate towards other imaginaries, rooted as well in the histories of the green city and of the intermediary scale open morphology. In these imaginaries, the plots5, the street6, the court7, or even the private garden8, participate in various scenarios of free space partitioning, between the individual and the collective whole. Finally, to expand the research field will serve to enrich the contemporary urbanism theories that pertain to free spaces, whose plurality of characters, uses and sensations we plead for. The term "urban villa"9 contains a semantic paradox full of promises. In its loneliness, the urban villa represents the individuality dreamt of by many multi-unit housing inhabitants. As the villa gets isolated from neighbouring houses and from the street, however, it is also a dialectical object, which liberates its surroundings while at the same time depending on them. On the one hand, its four elevations tend to open themselves generously towards the sun and to the views. On the other hand, in the case of dense groups of villas – which interests us most here, as it is the major trend in contemporary suburban context –, the free space is valued as a possession tightly shared. This is done in a very distinct way as in the compact city, and the urban villa becomes a particularly demanding performer/Schau-spielerin in matters of living and dwelling together. In such open urbanity forms, the closed universe of private life and the open one of the shared landscapes interact in a totally different way than in the modern scattered green city, particularly with regard to narrow density interactions and juxtapositions. The starting point of our research is to postulate that these interactions are able to generate an urban spatial tissue of high quality. The main objective is to recognize, to expose and to analyse the spatial modalities, architectural as well as scenic, through which this aim can be achieved. ________________________________________________ 1 Martin Steinmann, "Sinnliche Dichte, Die neue Bedeutung eines alten Wohntyps", werk, bauen + wohnen, n°10, 2002, pp. 10-19. 2 EPFL-ENAC-LHab, Prof. Martin Steinmann (direction) and Didier Challand (organisation), La villa urbaine : Exhibition, EPFL, 12-28 January 2004 ; seminar, 15 January 2004, with the participation of Martin Steinmann, Bruno Marchand, Adrian Meyer, Martin Hofer (Wüest+Partner), Didier Challand. 3 EPFL-ENAC-LHab (Laboratoire de l'Habitation Urbaine), Prof. Martin Steinmann, 3rd and 4th year. Winter 2002-2003; Villas urbaines - Le Clos Veyrassat, Rolle/VD ; Winter 2003-2004 ; Villas urbaines - Les Gönhardgüter in Aarau. 4 "imaginaire nemourien", in reference to Le Corbusier's sketch for Nemours, Algeria (around 1935) 5 We propose some examples around each topic, here : Brauerquartier, Winterthur (Blatter, Meili, Lerch, 1898-1899) 6 Une Cité Industrielle, Quartiers d'habitation en commun (Tony Garnier, between 1904 and 1917) 7 Quartiere operaio della Società Umanitaria, dit alle Rottole, Milan, (Giovanni Broglio, 1909) 8 Quartiers modernes Frugès, Pessac (Le Corbusier, 1925-1926) 9 The contemporary use of this term started from the late 70s in West Berlin and was stimulated by O. M. Ungers, H. Kollhoff and A. Ovaska.

EPFL2010