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PLK1 is a serine/threonine kinase with crucial roles during mitosis. However, its involvement during mammalian male meiosis remains largely unexplored. By inhibiting the kinase activity of PLK1 using BI 2536 on organotypic cultures of seminiferous tubules, we found that the disassembly of SYCP3 and HORMAD1 from the lateral elements of the synaptonemal complex during diakinesis is impeded. We also found that the normal recruitment of SYCP3 and HORMAD1 to the inner centromere in prometaphase I spermatocytes did not occur. Additionally, we analyzed the participation of PLK1 in the assembly of the inner centromere by studying its implication in the Bub1-H2AT120ph-dependent recruitment of shugoshin SGO2, and the Haspin-H3T3ph-dependent recruitment of Aurora B/C and Borealin. Our results indicated that both pathways are regulated by PLK1. Altogether, our results demonstrate that PLK1 is a master regulator of the late prophase I/metaphase I transition in mouse spermatocytes.

Cohesin cofactors regulate the loading, maintenance, and release of cohesin complexes from chromosomes during mitosis but little is known on their role during vertebrate meiosis. One such cofactor is PDS5, which exists as two paralogs in somatic and germline cells,PDS5A and PDS5B, with unclear functions. Here, we have analyzed their distribution and functions in mouse spermatocytes. We show that simultaneous excision of Pds5A and Pds5B results in severe defects during early prophase I while their individual depletion does not, suggesting their functional redundancy. Shortened axial/lateral elements and a reduction of early recombination nodules are observed after the strong depletion of PDS5A/B proteins. Moreover,telomere integrity and their association to the nuclear envelope are severely compromised. As these defects occur without detectable reduction in chromosome-bound cohesin, we propose that the dynamic behavior of the complex, mediated by PDS5 proteins, is key for successful completion of meiotic prophase I.

[EN] Post-injection fuel dribble is known to lead to incomplete atomisation and combustion due to the release of slow-moving, and often surface-bound, liquid fuel after the end of injection. This can have a negative effect on engine emissions, performance and injector durability. To better quantify this phenomenon, we developed an image-processing approach to measure the volume of ligaments produced during the end of injection. We applied our processing approach to an Engine Combustion Network 'Spray B' 3-hole injector, using datasets from 220 injections generated by different research groups, to decouple the effect of gas temperature and pressure on the fuel dribble process. High-speed X-ray phase-contrast images obtained at room temperature conditions (297 K) at the Advanced Photon Source at Argonne National Laboratory, together with diffused back-illumination images captured at a wide range of temperature conditions (293-900 K) by CMT Motores Termicos were analysed and compared quantitatively. We found a good agreement between image sets obtained by Argonne National Laboratory and CMT Motores Termicos using different imaging techniques. The maximum dribble volume within the field of view of the imaging system and the mean rate of fuel dribble were considered as characteristic parameters of the fuel dribble process. Analysis showed that the absolute mean dribble rate increases with temperature when injection pressure is higher than 1000 bar and slightly decreases at high injection pressures (>500 bar) when temperature is close to 293 K. Larger maximum volumes of the fuel dribble were observed at lower gas temperatures (similar to 473 K) and low gas pressures (<30 bar), with a slight dependence on injection pressure.

[EN] Multiple injection strategies have increased their capabilities along with the evolution of injection system technologies up to the point that nowadays it is possible to inject eight different pulses, permitting to improve the engine performance, and consequently, emissions. The present work was realized for two simplified strategies: a pilot-main and a main-post, in order to analyze the influence of an auxiliary pulse on the main and otherwise, in reactive conditions for two pilot/post quantities and four hydraulic dwell times. The study was carried out by employing two optical techniques: diffused back-illumination with flame bandpass chemiluminescence for measuring soot, represented by soot-maps distribution, and single-pass schlieren for ignition delay (ID). Furthermore, a novel methodology for decoupling the start of combustion (SOC) of the second pulse was developed and successfully validated. From the ignition delay results, it was found for all test points that the pilot injection enhanced conditions, which promote a faster ignition of the main pulse, also at higher chamber temperatures, all conditions presented a separate combustion event for each injection. In emission terms, soot increased in the pilot-main strategies compared to its single injection case, as well as, in conditions that promote faster-premixed combustion.

[EN] Multiple injection strategies have contributed to the improvement of thermal processes in Internal Combustion Engines. On this matter, the correct performance of the injector is a critical factor in the implementation of these techniques, as changes in the behavior of the injector could affect the injection development, altering the combustion process and heat transformation efficiency. Thus, the present study analyzes the development of multiple injection events in a diesel injector aged due to partial obstruction of the holes of the nozzle. To this end, a multi-hole piezoelectric injector was employed, in which the aging of the injector is evaluated through momentum flux measurements for each hole. Afterwards, rate of injection tests with pilot and post injection strategies are performed, and the results are compared to the injection events made by the same injector before aging. The results provided by the momentum flux experiments confirmed the partial obstruction of two holes. Furthermore, rate of injection comparisons showed that the injector had a lower steady-state rate of injection after aging and required a longer time to end the injection. These phenomena affected the multiple injection events, as the extended time required to end the injection reduced the hydraulic dwell time between pilot/post injection and the main injection. Furthermore, for short dwell times, this phenomenon led to the unification of the main and post injection, resulting in a large single injection. Hence, not only an increase in fuel consumption would appear, but the thermal benefits of implementing the post injection would be lost.

[EN] Internal combustion engines have witnessed an ever increasing stringency in emission limits and fuel economy regulations that has continuously provoked researchers to develop complex strategies that enables engines to cope with these standards. Optical techniques have been a viable method in the study of thermal processes occurring inside internal combustion engines and provides researchers with a solid understanding of the heat and mass transfer taking place. In particular, the current study utilizes two optical techniques, diffused back illumination and schlieren imaging, to visualize the spray behavior in multiple injection strategies of evaporative diesel sprays. A novel method has been developed in order to couple the two optical techniques to visualize both liquid and vapor phases of either pilot-main and main-post injections. The influence of the auxiliary injections on the main, and vice versa, in terms of spray segmentation and spray development has been studied for two different pilot/post quantities and four hydraulic dwell times under two different chamber conditions. The spray development displayed no effect of pilot quantity and dwell time on the liquid length of the second injection. On the other hand, a more pronoun effect on the vapor phase penetration and spreading angle was evidenced by the pilot injection where the main injection has penetrated farther with a higher spreading angle as compared to the case with a single injection event. The understanding of multiple injection is thus fundamental for the improvement of thermal processes in Internal Combustion Engines.