Nation state | EPFL Graph Search

A nation-state is a political unit where the state, a centralized political organization ruling over a population within a territory, and the nation, a community based on a common identity, are congruent. It is a more precise concept than "country", since a country does not need to have a predominant national or ethnic group. A nation, sometimes used in the sense of a common ethnicity, may include a diaspora or refugees who live outside the nation-state; some nations of this sense do not have a state where that ethnicity predominates. In a more general sense, a nation-state is simply a large, politically sovereign country or administrative territory. A nation-state may be contrasted with:

An empire, a political unit made up of several territories and peoples, typically established through conquest and marked by a dominant center and subordinate peripheries
A multinational state, where no one ethnic group dominates (such a state may also be considered a multicultural state de

Géohistoire de l'Albanie moderne. Une lecture des recensements de 1918 à 2011.

Alain Nicolas Jarne

In this thesis, an original database is constituted, described and exploited in a geohistorical perspective, containing the registration of the population at the local level for the fifteen censuses conducted in Albania between 1918 and 2011. The precision of the spatialization makes possible the diachronic comparability of statistical data in this country marked by numerous territorial-administrative reforms, thus allowing a new look at certain aspects of its history. A detailed description is given of the spatial dynamics and mutations at work beyond the four major systems that have succeeded one another in Albania's modern history : integration into the Ottoman networks ; geopolitical confrontation that saw the disappearance of empires in favour of nation-States ; half a century of communism characterised by its progressive introversion and original territorial development ; and finally the brutal inclusion in the liberal economy that produced sharp emigration and rural decline, consecrating the irresistible emergence of the metropolis-capital. The data are modulated according to a whole range of regionalisations and typologies of territory, making it possible to situate mobilities and the different phases of urbanisation in their spatial, political and cultural contexts. Cartography plays a key role, revealing spatial structures on unprecedented scales. The approach is alternately nomothetic - observation and detection of regularities, contrasts and breaks in the growth rates visible in the various aggregates and on the maps - and hypothetico-deductive : many hypotheses suggested by the literature (identification of migration chains, specificity of Albanian underurbanization, existence of diverted migration towards the outskirts of cities at the end of communism, political dimension of metropolization, etc.) are revisited on the basis of the corpus of the thesis. The last two censuses (2001 and 2011) are used to reconstruct with great spatial accuracy the succession of migrations between the 1950s and 2011. The strong historicity of the Albanian trajectory is confronted with some classical models of the modernization paradigm : vital and mobility transitions or the emergence of the World-Society. The geohistorical narrative takes the conventional form of describing a succession of spatial systems and the transitions between them. The end of the thesis contains a different theoretical proposition centered on the concept of mobility geotype. Conceived as a historically significant form of mobility that is recognizable by the regularity and duration of its spatial signature, the mobility geotype lies on a gradient from social reproduction (e.g., marriage spatial patterns) to radical change (crossing of important social boundaries, disruption of the order of co-presences, such as during distant emigration). This property is referred to as histority (dialectic of reproduction and social change). Such an alternative approach is introduced, along with a discussion of its advantages - such as a richer conception of time - and its possible operationalisation in the context of a geohistorical approach. A histority calculation is proposed on the basis of urbanity differentials between the origins and destinations of Albanian migrations.

EPFL2020

Geological characterization of cataclastic rock samples using medical X-ray computerized tomography

Pierre Guillaume Christe

Technical difficulties associated with tunnelling operations in tectonized geological settings are frequently encountered. They may include instantaneous and delayed cavity convergence, sudden collapse of walls or roof of a gallery, outpouring of fault-filling materials and water inflows. These phenomena may negatively affect economical and safety aspects of construction sites. The present study refers to two previous research projects conducted at the EPFL addressing the problem of an improved geological and geomechanical characterization of weak cataclastic rocks in underground excavation works (Cataclastic fault rocks in underground excavations, a geological perspective, Bürgi, 1999; Caractérisation géomécanique de roches cataclastiques rencontrées dans des ouvrages souterrains alpins, Habimana, 1999). Cataclasis is an evolutionary rock degradation process in time and magnitude related to fault zone activity in the Earth's crust. A conceptual model describing the occurrence and variability of cataclastic rocks at shallow crustal conditions is proposed in this research. It describes environment of fault zones based on both theoretical considerations and field experiences collected during self-realized short-drilling operations performed in contrasted petrological settings. The model considers cataclasis from a regional perspective (macroscopic scale) down to its microscopic manifestations on rock materials. Cataclastic rock characteristics are strongly influenced by the degree of tectonic solicitation and the initial rock composition. Guidelines about specific damage microstructures diagnostic of the cataclastic intensity and function of the initial rock protolith can meaningfully assist the interpretation of rock specimens recovered from reconnaissance drilling operations. Despite the poor mechanical quality often observed for such samples and their readiness to collapse, this study demonstrates that the in situ extraction of cataclastic specimens can be largely improved with the use of a high-quality drilling equipment. Accordingly, with the availability of representative materials for subsequent studies, the uncertainties affecting the geological prognosis can be strongly limited at a preliminary stage of geotechnical studies. It is shown that the geotechnical characterisation of cataclastic rock cores by means of laboratory investigations requires combining information about rock microstructure and mineralogy with strain-stress relationship derived from triaxial compression tests. Such a framework makes it possible to interpret and explain the specific mechanical behavior of heterogeneous-anisotropic rock materials in a much more coherent manner. With this regard, the approach followed by Bürgi (1999) with a mineralo-structural index (MSI) determined on 2D thin sections and proposed to predict cataclastic rock strength based on geological evidences, is found to have potential for geotechnical studies. However, Bürgi's approach still faces heavy criticism in the light of the practical application. Its limitations are detailed and discussed in this study. Accounting for both aspects of the rock characterization procedure, an operational methodology is therefore proposed aiming at its application in geotechnical studies. The medical X-ray computerized tomography (XRCT) has been specifically implemented in this context for the analysis of geotechnical rock cores, as a non-destructive technique which allows a rapid indirect imaging of the rock core structure before any further analytical manipulations are conducted. The technique is found facilitating to a great extent the study of cataclastic materials. An irradiation protocol has been defined and an acquisition strategy minimalizing inherent artifacts of the XRCT technique has been tested. Obtained results are highly encouraging. Moreover, an image analysis tool has been developed in order to improve the segmentation of geological damage features from indirectly recorded X-ray models. As discussed in details within this study, a critical analysis of 3D segmented models corresponding to sample structures before and after mechanical tests is thought to be capable to improve the triaxial test interpretation. The XRCT is therefore envisaged as a bridge technique permitting an improved correlation between specific properties of cataclastic rocks based on indirect evidences. With it, the geological and mechanical characterizations can be performed on the exactly same samples, reducing uncertainty in the characterization procedure. This step goes towards the development of a precise geotechnical classification for cataclastic rocks. Based on the XRCT technique, it is also discussed how Bürgi's approach could be translated in a three-dimensional form to reach a wider agreement. Based on a database of carbonatic cataclasites, it is evidenced that cataclastic strength and deformation properties are strongly influenced by textural and structural characteristics of pre-existing damage microstructures. Strength data obtained in this research show that in the same fault zone environment, different mode of deformations affect cataclastic rocks and that peak triaxial strength can vary significantly. Heterogeneity and material anisotropy are prime factors affecting specific behaviors of cataclastic rocks. Therefore, it is suggested to incorporate geological features into constitutive frameworks which describe mechanical behavior of such materials. This last aspect constitutes a very stimulating research field where further work is needed today.

EPFL2009

Phase separation of self-propelled disks with ferromagnetic and nematic alignment

Ignacio Pagonabarraga Mora, Elena Sesé Sansa

We present a comprehensive study of a model system of repulsive self-propelled disks in two dimensions with ferromagnetic and nematic velocity alignment interactions. We characterize the phase behavior of the system as a function of the alignment and self-propulsion strength, featuring orientational order for strong alignment and motility-induced phase separation (MIPS) at moderate alignment but high enough self-propulsion. We derive a microscopic theory for these systems yielding a closed set of hydrodynamic equations from which we perform a linear stability analysis of the homogenous disordered state. This analysis predicts MIPS in the presence of aligning torques. The nature of the continuum theory allows for an explicit quantitative comparison with particle-based simulations, which consistently shows that ferromagnetic alignment fosters phase separation, while nematic alignment does not alter either the nature or the location of the instability responsible for it. In the ferromagnetic case, such behavior is due to an increase of the imbalance of the number of particle collisions along different orientations, giving rise to the self-trapping of particles along their self-propulsion direction. On the contrary, the anisotropy of the pair correlation function, which encodes this self-trapping effect, is not significantly affected by nematic torques. Our work shows the predictive power of such microscopic theories to describe complex active matter systems with different interaction symmetries and sheds light on the impact of velocity-alignment interactions in motility-induced phase separation.