An efficient algorithm for computing the distance between close partitions

A K -partition of a set S is a splitting of S into K non-overlapping classes that cover all elements of S . Numerous practical applications dealing with data partitioning or clustering require computing the distance between two partitions. Previous articles proved that one can compute it in polynomial time—minimum O ( | S | + K 2 ) and maximum O ( | S | + K 3 ) —using a reduction to the linear assignment problem. We propose several conditions for which the partition distance can be computed in O ( | S | ) time. In practical terms, this computation can be done in O ( | S | ) time for any two relatively resembling partitions (i.e. with distance less than | S | 5 ) except specially constructed cases. Finally, we prove that, even if there is a bounded number of classes for which the proposed conditions are not satisfied, one can still preserve the linear complexity by exploiting decomposition properties of the similarity matrix

Informed Reactive Tabu Search for Graph Coloring

Tabu search (TS) has always been a very popular algorithm for graph coloring, both as a stand-alone optimizer as well as a subroutine inside population-based hybrid methods. We present two TS extensions that could allow previous TS algorithms to improve their behavior at almost no additional computational cost. First, we integrate two new evaluation functions which employ supplementary (structural or dynamic) information in addition to the conventional objective function (the number of edges with both ends of the same color). These new evaluation functions allow the search process to differentiate configurations not distinguished by the conventional evaluation function. The second extension concerns a reactive mechanism for improving the tabu list management. Theoretical arguments show that this reactive component completely eliminates the risk of getting blocked looping on plateaus. Numerical experiments show that the two proposed TS extensions can be very useful inside a stand-alone TS optimizer, as well as inside TS subroutines of state-of-the-art hybrid methods.

Experimental combustion chamber simulation at transient regimes

The transient regimes in a combustion chamber has to be as short as possible because flame front position and thickness can destroy the combustion chamber in couple seconds. The simulation of such a regime has to be performed unsteady. An experimental combustion chamber it is simulated at two unsteady regimes to see the flame front structure and comparison it is made with the experimental data to validate the results. For this analysis Ansys CFX was used and the turbulent model was DES while the combustion model was Eddy Dissipation. The two cases show different flame front structures while the boundary conditions for the two regimes are very similar

Experimental measurements in Hartman oscillators

The paper presents high frequency pointwise measurements of pressure and temperature carried out on a shock wave generator consisting of a couple of supersonic jets impinging on a Hartman oscillator system. The shock wave generator was developed as a means to achieve an aerodynamically controlled pulsed detonation chamber. The analysis allows the selection of the optimal geometry and inlet conditions for such an application. The effect of the inlet conditions and of the geometry of the experimental model on the frequency and amplitude of the pressure waves occurring in the system is analyzed. The paper also presents the effects of other geometrical parameters: the critical section of the jet nozzles, the volume ratio of the resonator geometry, and the inlet angles of the jets. Effects of inlet pressure and temperature are also included

Experimental approach regarding the ignition of H2/O2 mixtures in vacuum environment

The paper, elaborated in the framework of the ESA activity "Green thruster for attitude control and orbital manoeuvres of small satellites (GREENTH)", focuses on the preliminary stages of an experimental program aiming to evaluate the feasibility and to increase the maturity level of a H2/O2 pulsed technology for small scale space propulsion applications. For demonstrating the capability of the H2/O2 mixture to be pulsed and ignited in a vacuum environment, the paper presents the main technical requirements, some addressing the thruster itself, related to system dimensioning, such as the nature of manoeuvres, the thrust level, the minimum impulse bit, the operating conditions, and some addressing the experimental campaign to be performed. The design of the experimental installation has taken into account the demands coming for the challenges and limitations raised by the small-scale satellites (telecommunications satellites or even CubeSats) applications, including vacuum system dimensioning, injection and ignition systems dimensioning and equipment and instrumentation specifications. The testing program covers the selected ranges of operational parameters and the operating sequences, for pulse mode and steady state tests, in order to determine the performance level and to evaluate the pulse repeatability, respectively to demonstrate the process stability

Increasing the Creativity of ENGINO Toy Sets and Generating Automatic Building Instructions

During the First Study Group with Industry which was held in Limassol, Cyprus, the ENGINO⃝R TOY SYSTEM introduced two challenging problems. The first is to get bounds on the number of possible models/toys which can be constructed using a given package of building blocks. And the second is to generate automatically the assembly instructions for a given toy. In this report we summarize our insights and provide preliminary results for the two challenges