A novel Rac1-GSPT1 signaling pathway controls astrogliosis following central nervous system injury

Astrogliosis (i.e. glial scar), which is comprised primarily of proliferated astrocytes at the lesion site and migrated astrocytes from neighboring regions, is one of the key reactions in determining outcomes after CNS injury. In an effort to identify potential molecules/pathways that regulate astrogliosis, we sought to determine whether Rac/Rac-mediated signaling in astrocytes represents a novel candidate for therapeutic intervention following CNS injury. For these studies, we generated mice with Rac1 deletion under the control of the GFAP (glial fibrillary acidic protein) promoter (GFAP-Cre;Rac1(flox/flox)). GFAP-Cre;Rac1(flox/flox) (Rac1-KO) mice exhibited better recovery after spinal cord injury and exhibited reduced astrogliosis at the lesion site relative to control. Reduced astrogliosis was also observed in Rac1-KO mice following microbeam irradiation-induced injury. Moreover, knockdown (KD) or KO of Rac1 in astrocytes (LN229 cells, primary astrocytes, or primary astrocytes from Rac1-KO mice) led to delayed cell cycle progression and reduced cell migration. Rac1-KD or Rac1-KO astrocytes additionally had decreased levels of GSPT1 (G(1) to S phase transition 1) expression and reduced responses of IL-1β and GSPT1 to LPS treatment, indicating that IL-1β and GSPT1 are downstream molecules of Rac1 associated with inflammatory condition. Furthermore, GSPT1-KD astrocytes had cell cycle delay, with no effect on cell migration. The cell cycle delay induced by Rac1-KD was rescued by overexpression of GSPT1. Based on these results, we propose that Rac1-GSPT1 represents a novel signaling axis in astrocytes that accelerates proliferation in response to inflammation, which is one important factor in the development of astrogliosis/glial scar following CNS injury

Investigation on Ignition Coil Specification for Dilution Combustion System

To improve thermal efficiency of internal combustion engine, dilution combustion system, such as lean burn and Exhaust Gas Recirculation (EGR) system, have been developed with spark ignition coils generating large discharge current and energy. Several researches have clarified that large discharge current increases discharge channel stretch and decreases possibility of discharge channel blow-off and misfire. However, these investigations don\u27t mention effect of discharge current profile on combustion speed and discharge channel behaviour enough. Purpose of this research is to investigate relation among dilution rate, combustion speed, discharge channel behaviour and discharge current. To achieve this purpose, five coils having different current profiles were evaluated by combustion test and in-cylinder optical measurement test with research single cylinder engine. The combustion test results showed a correlation between dilution limit and initial combustion period. And optical measurement test results showed a correlation of initial combustion period with discharge channel stretch. Moreover, saturation of discharge channel stretch were observed from a certain discharge current value on up. Based on these results, adequate coil for dilution system was selected. Finally, the coil was equipped on a vehicle and performance test was conducted. The vehicle with LP-EGR system was stably driven with 18% of EGR rate, and 2.3% of fuel reduction rate were verified in the WLTC mode. The selected high energy ignition coil was contributing reduction of misfire during EGR operation

Modeling wall film formation and vaporization of a gasoline surrogate fuel

To simulate the wall film formation and vaporization processes in gasoline direct-injection spark-ignition engines including considerations of the physical properties and vapor-liquid equilibrium of multi-component fuels, spray-wall interaction sub-models were implemented with the 3D-CFD software HINOCA which has been developed for automotive engine cylinder simulations. The models used were the Senda model for spray-wall impingement including splash, deposition, droplet-droplet interactions, and droplet-film interactions; the O'Rourke model for heat transfer and film vaporization; a simple film flow model considering momentum conservation; and Raoult's law for vapor-liquid equilibrium. First, the model validated the calculated results for a single-component fuel (iso-octane) through comparisons with experimental data in terms of wall film area and heat flux between the wall and film. Second, numerical simulations were conducted with a 5-component gasoline surrogate fuel which was designed taking into account the average octane number, aromatic content, and distillation characteristic. The results showed clear differences in the contributions of the 5 components to the wall film, and the possibility that the aromatic content with higher carbon atoms could be a source of soot formation

Identification of Suitable Ignition Conditions for Stable Switch from SI to HCCI of a Blowdown Supercharged Engine

In this paper, the necessary in-cylinder conditions for the transition from spark ignion (SI) to homogeneous charge compression ignition (HCCI) are analyzed. The hereby important factors for ignition time are investigated analytically. A control oriented combustion model, that is validated by experimental data, is used for sensivity analysis and a Monte-Carlo approach is taken to identify the important factors for transient HCCI and combustion mode switch. As a result, it was shown that the in-cylinder temperature plays a major role, exceeding other factors, such as the air-fuel ratio. The analytical conclusions are illustrated by numerical simulations after which the feasibility for actuation will be discussed. Final goal is to ensure a stable combustion in each cycle without crossing unstable combustion conditions

Control-Oriented Modeling and Model-Based Control of a Blowdown Supercharge (BDSC) HCCI Engine

Closed-loop control is vital for an application of HCCI engines in passenger cars. This paper introduces a simplified control-oriented model for control of combustion phasing and IMEP of a Blowdown Supercharge Engine (BDSC). Despite the complexity of this particular engine, the model has been found to match not only the steady state values in high load HCCI, but also to reproduce the transients. This model takes advantage of the knowledge of non-dynamic processes within the engine that can be derived from steady state values, while the main dynamics are achieved by dynamically modelling of cyclic coupling via in-cylinder temperature alone and mean exhaust pressure dynamics. Furthermore, a simplified combustion model has been found to be accurate enough for the region of interest. An automated tuning scheme helps to match the model to the respective target values. With this model and the tuning scheme, the model can be easily tuned for every possible case. A model-based MIMO state controller, based on Sliding-Mode Control theory has been designed and tested on a detailed 1-D simulation code

Study of Discharge Characteristics on Ignition Performance via High-Speed Imaging in a CVCC

Advanced combustion technologies, like highly boosted and lean or dilute combustion, have been employed to meet the demands of high efficiency and low emissions in SI engines, which have increased the challenges of ignition control. It is essential to find a suitable ignition strategy due to the need to develop a next-generation spark ignition system. In this study, simultaneous visualization by a high-speed infrared camera (FLIR X6900sc) and a conventional high-speed camera (FASTCAM SA-X) is carried out to obtain deeper insights into the ignition process in a constant volume combustion chamber (CVCC). Infrared images have provided a more accurate way of measuring the initial flame and are able to analyze quantitatively. Ignition performance is studied with various mixture dilutions, flow conditions, and discharge characteristics. Two types of ignition coils that have the same discharge energy were analyzed in particular. The results show that extending the discharge duration is more helpful in improving the ignition performance under the increasing dilution ratio, compared to the enhanced discharge current at the same discharge energy. However, the discharge current plays a more vital role in perfecting the ignition performance under the increasing local flow velocity than the discharge duration

Study of Discharge Characteristics on Ignition Performance via High-Speed Imaging in a CVCC

Advanced combustion technologies, like highly boosted and lean or dilute combustion, have been employed to meet the demands of high efficiency and low emissions in SI engines, which have increased the challenges of ignition control. It is essential to find a suitable ignition strategy due to the need to develop a next-generation spark ignition system. In this study, simultaneous visualization by a high-speed infrared camera (FLIR X6900sc) and a conventional high-speed camera (FASTCAM SA-X) is carried out to obtain deeper insights into the ignition process in a constant volume combustion chamber (CVCC). Infrared images have provided a more accurate way of measuring the initial flame and are able to analyze quantitatively. Ignition performance is studied with various mixture dilutions, flow conditions, and discharge characteristics. Two types of ignition coils that have the same discharge energy were analyzed in particular. The results show that extending the discharge duration is more helpful in improving the ignition performance under the increasing dilution ratio, compared to the enhanced discharge current at the same discharge energy. However, the discharge current plays a more vital role in perfecting the ignition performance under the increasing local flow velocity than the discharge duration