Dust and gas emission from cometary nuclei: the case of comet 67P/Churyumov-Gerasimenko

Comets display with decreasing solar distance an increased emission of gas and dust particles, leading to the formation of the coma and tail. Spacecraft missions provide insight in the temporal and spatial variations of the dust and gas sources located on the cometary nucleus. For the case of comet 67P/Churyumov-Gerasimenko (67P/C-G), the long-term observations from the Rosetta mission point to a homogeneous dust emission across the entire illuminated surface. Despite the homogeneous initial distribution, a collimation in jet-like structures becomes visible. We propose that this observation is linked directly to the complex shape of the nucleus and projects concave topographical features into the dust coma. To test this hypothesis, we put forward a gas-dust description of 67P/C-G, where gravitational and gas forces are accurately determined from the surface mesh and the rotation of the nucleus is fully incorporated. The emerging jet-like structures persist for a wide range of gas-dust interactions and show a dust velocity dependent bending.Comment: 17 pages, with 7 figures. To appear in Advances in Physics X (2018

KPZ-type fluctuation bounds for interacting diffusions in equilibrium

We study the fluctuations in equilibrium of a class of Brownian motions interacting through a potential. For a certain choice of exponential potential, the distribution of the system coincides with differences of free energies of the stationary semi-discrete or O'Connell-Yor polymer. We show that for Gaussian potentials, the fluctuations are of order $N^{\frac{1}{4}}$ when the time and system size coincide, whereas for a class of more general convex potentials $V$ the fluctuations are of order at most $N^{\frac{1}{3}}$. In the O'Connell-Yor case, we recover the known upper bounds for the fluctuation exponents using a dynamical approach, without reference to the polymer partition function interpretation.Comment: 43 page

Die sibirischen Bucharioten

Les Boukhares de Sibérie. – Avant la conquête et la colonisation de la Sibérie par la Russie, la plaine de Sibérie occidentale faisait partie de l’Empire de la Horde d’Or. Le khanat de Sibir, l’une des formations politiques héritières de la Horde d’Or, était une principauté contrôlée par les khans uzbeks pendant les xve et xvie siècles. Les pratiques commerciales des Boukhares de Sibérie, un groupe restreint mais fortuné originaire d’Asie Centrale, instaurèrent des liens économiques et culturels étroits entre la Sibérie occidentale et le monde islamique qui était aussi sous domination russe. Dans cet article nous examinons l’histoire des Boukhares de Sibérie, une « diaspora réduite et très mobile » (J. Armstrong) pendant la période de la domination russe ainsi que l’extension et l’importance de leur commerce avec l’Orient entre les xvie et xixe siècles. Devant les difficultés pour la Russie de développer la Sibérie, les autorités reconnurent la nécessité des activités économiques de la petite élite musulmane et lui accordèrent une série de privilèges substantiels. Les Boukhares purent ainsi préserver leur potentiel économique et leurs traits culturels particuliers jusqu’au début du xixe siècle. Sous la domination russe, ils se posèrent en couche supérieure de la société musulmane locale.The Siberian Bukhariots. – Prior to Russian conquest and settlement the western Siberian plains formed part of the Empire of the Golden Horde. One of the Horde’s successor states was the khanate of Sibir, a principality controlled by Uzbek khans throughout the fifteenth and sixteenth centuries. Trade operations of the Siberian Bukhariots, a small but wealthy group of Central Asian origin, secured close economic and cultural bonds between western Siberia and the Islamic world, also under Russian rule. This article traces the history of the Bukhariots as a small and highly “mobile diaspora” (J. Armstrong) under Russian rule and examines the range and importance of their Oriental trade from the sixteenth to the nineteenth centuries. Given the limited Russian potential for the development of Siberia, state authorities recognized the indispensability of the small Muslim elite’s economic activities and furnished them with substantial privileges. The Bukhariots could thus preserve their economic potential and their particular cultural features until the early nineteenth century. Under Russian rule, they firmly established themselves as the upper strata within the local Muslim society

Muslim Religious Institutions in Imperial Russia. The Islamic World of the Novouzensk District and the Kazakh Inner Horde, 1780-1910. Leiden - Boston - Köln, Brill, 2001 (Islamic History and Civilization, 35), x-341 p.

The last two decades of the 20th century witnessed an important shift in Russian studies from the centre to the peripheries. Historical research focussed on local societies, Russian and even more so non-Russian. Due to the lack of indigenous sources or inadequate knowledge of minority languages, a good portion of recent research, however, continued to rely primarily on Russian sources. The historiographical boom in ethnic and national studies thus did not always contribute to a critical reapp..