In data centres, there exist several techniques for energy efficiency purposes. When applied, most of those techniques have impact on the quality (e.g. performance) of the underlying services. A careful study is required in order to optimise such an energy-performance trade-off. In this paper, we study the speed scaling as an energy efficiency technique within the scope of high-performance computing (HPC) data centres. We propose a methodology based on threelevels: analytic, simulation and technical. At the analytical level, the matrix-analytic method (MAM) allows one to obtain energyperformance measures explicitly for a small-scale system. At the simulation level, discrete-event simulation (DES) based on the generalised semi-Markov processes (GSMP) is used to derive the corresponding estimates. Finally, at the technical level, a real small-scaled system in a controlled environment is used. The preliminary results demonstrate that simulation and technical models go well together with the theoretical one with an accuracy of more than 95%. CCS CONCEPTS• Hardware → Enterprise level and data centers power issues; • Mathematics of computing → Queueing theory; • Computing methodologies → Discrete-event simulation.

Expression of gene of arginine deiminase (AD) allows adaptation of Streptococcus pyogenes to adverse environmental conditions. AD activity can lead to L‐arginine deficiency in the host cells’ microenvironment. Bioavailability of L‐arginine is an important factor regulating the functions of the immune cells in mammals. By introducing a mutation into S pyogenes M46‐16, we obtained a strain with inactivated arcA/sagp gene (M49‐16 delArcA), deficient in AD. This allowed elucidating the function of AD in pathogenesis of streptococcal infection. The virulence of the parental and mutant strains was examined in a murine model of subcutaneous streptococcal infection. L‐arginine concentration in the plasma of mice infected with S pyogenes M49‐16 delArcA remained unchanged in course of the entire experiment. At the same time mice infected with S pyogenes M49‐16 demonstrated gradual diminution of L‐arginine concentration in the blood plasma, which might be due to the activity of streptococcal AD. Mice infected with S pyogenes M49‐16 delArcA demonstrated less intensive bacterial growth in the primary foci and less pronounced bacterial dissemination as compared with animals infected with the parental strain S pyogenes M46‐16. Similarly, thymus involution, alterations in apoptosis, thymocyte subsets and Treg cells differentiation were less pronounced in mice infected with S pyogenes M49‐16 delArcA than in those infected with the parental strain. The results obtained showed that S pyogenes M49‐16 delArcA, unable to produce AD, had reduced virulence in comparison with the parental S pyogenes M49‐16 strain. AD is an important factor for the realization of the pathogenic potential of streptococci.

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Positive DC breakdown voltages of various NZ-02 gas mixtures have been measured with point-to-plane gaps over a temperature range 293 K-113 K, the gas density being kept constant at any temperature. The breakdown voltage in Nz increased at low temperatures. The increase in breakdown voltages became small, when a small amount of O Z (less than 1 %) was mixed into Nz. The breakdown voltage in synthetic air decreased at low temperatures. When small pulses were superposed on DC voltages, the breakdown voltage changes only slightly with temperature in both Nz and synthetic air.