Self-Sustained Reaction Fronts in Porous Media

We analyze experimentally chemical waves propagation in the disordered flow field of a porous medium. The reaction fronts travel at a constant velocity which drastically depends on the mean flow direction and rate. The fronts may propagate either downstream and upstream but, surprisingly, they remain static over a range of flow rate values. Resulting from the competition between the chemical reaction and the disordered flow field, these frozen fronts display a particular sawtooth shape. The frozen regime is likely to be associated with front pinning in low velocity zones, the number of which varies with the ratio of the mean flow and the chemical front velocities.Comment: 4 pages, 5 figure

Dynamics of ethnic structures in the Baltic States

The aim of this article is to present changes in the three Baltic States (Estonia, Latvia and Lithuania) and to analyse the demographic developments of the titular ethnicities and ethnic minorities. In all censuses carried out in the Baltics, including the 2000-2001 and 2011 censuses, respondents were asked to name their ethnic identity. This gave basic information for study of ethnic composition and the characteristics of ethnic Estonians, Latvians and Lithuanians and other ethnic groups living in the Baltics. The article reports from study of ethnic developments since the regained political independence in the beginning of the 1990s and more detailed in the last decade. A sudden reversal of migration and natural reproduction processes changed the population proportion of titular ethnicities, Slavs and other minorities. In the 1990s and the beginning of this century the total number of population of ethnic Estonians, Latvians and Lithuanians has decreased; however, the proportion of titular ethnicities has increased. The Baltic States have one of the highest population loss indicators in the world. The excess of deaths over births has been since 1991, and emigration is strongly prevailing in international migration processes, particularly among minorities. However, even now minorities constitute one- fourth of the total in the Baltic population (in Latvia 38%, in the capital city Riga 54%). The age structure of minorities is relatively older than the structure of the titular ethnicities. The largest minorities by size are Russians, Poles (the greater majority of them reside in Lithuania), Belarussians and Ukrainians

Experimental evidence for three universality classes for reaction fronts in disordered flows

Self-sustained reaction fronts in a disordered medium subject to an external flow display self-affine roughening, pinning and depinning transitions. We measure spatial and temporal fluctuations of the front in $1+1$ dimensions, controlled by a single parameter, the mean flow velocity. Three distinct universality classes are observed, consistent with the Kardar-Parisi-Zhang (KPZ) class for fast advancing or receding fronts, the quenched KPZ class (positive-qKPZ) when the mean flow approximately cancels the reaction rate, and the negative-qKPZ class for slowly receding fronts. Both quenched KPZ classes exhibit distinct depinning transitions, in agreement with the theory

Size And High Temperature Effects On The Compressive Strength Of Self Compacting Concretes

The compressive strength behavior of concrete is one of the fundamental parameters of structural design as most load-bearing concrete elements, such as beams, columns and slabs. However, it was known that compressive behavior of the concrete elements alter depend on the element size and exposed temperature conditions. When the slenderness (height/diameter) of the concrete elements increased, compressive strength decreased relatively and this behavior known as size effect. In this study, compressive strength variation of the self compacting concrete specimens investigated taking in to account the different slenderness ratio and exposure temperatures. For this purpose, a self compacting mixture was prepared with water to cement ratio of 0.40 and 450 kg/m3 cement dosage. Cylindrical specimens with the diameter of 100 mm and slenderness of 2.0, 1.5, 1.0, and 0.5 were prepared and exposed to the different high temperatures (400, 600 and 800 oC) for an hour. For a control purpose, same size specimens were also tested under the laboratory conditions. The results show that high temperature exposure has severe strength loss effect on the concrete specimens irrespective of the slenderness ratio. Increasing the exposure temperature increased the strength loss of the specimens drastically. Moreover, it was seen that relative strength change (decrease) is evident when specimens' size increased

ProFuN TG:A Tool for Programming and Managing Performance-Aware Sensor Network Applications

Sensor network macroprogramming methodologies such as the Abstract Task Graph hold the promise of enabling high-level sensor network application development. However, progress in this area is hampered by the scarcity of tools, and also because of insufficient focus on developing tool support for programming applications aware of performance requirements. We present ProFuN TG (Task Graph), a tool for designing sensor network applications using task graphs. ProFuN TG provides automated task mapping, sensor node firmware macrocompilation, application simulation, deployment, and runtime maintenance capabilities. It allows users to incorporate performance requirements in the applications, expressed through constraints on task-to-task dataflows. The tool includes middleware that uses an efficient flooding-based protocol to set up tasks in the network, and also enables runtime assurance by keeping track of the constraint conditions. We show that the adaptive task reallocation enabled by our approach can significantly increase application reliability while decreasing energy consumption: in a network with unreliable links, we achieve above 99.89 % task-to-task PDR while keeping the maximal radio duty cycle around 2.0 %