Influence of rotational speed and torque on meshing efficiency of double helical gear transmission system

The accuracy of gear meshing efficiency model is the key to study the influence factors of gear meshing efficiency. Experiment is an effective method to verify the theory model. Therefore, the acquisition of experimental value of gear meshing efficiency is particularly important. Taken double helical gears as the research object, on the analysis of a large number of experimental data, the experimental value of gear meshing efficiency for double helical gears are calculated and then the influence of rotational speed and torque on meshing efficiency of double helical gears is studied. Firstly, the calculation method of transmission efficiency for experimental value in different layout of gear test-rigs with closed power flow is summarized. Secondly, the calculation method of meshing efficiency for experimental value in gear test-rig with closed power flow is introduced. Thirdly, the calculation method of load-dependent bearing loss is given. Finally, the experimental value of meshing efficiency for double helical gears is calculated and the influence of rotational speed and torque on meshing efficiency of double helical gears is obtained, which lays a theoretical foundation for the further improvement of the transmission efficiency of double helical gears.

Helping the Released Guardian: Drug Combinations for Supporting the Anticancer Activity of HDM2 (MDM2) Antagonists

The protein p53, known as the “Guardian of the Genome”, plays an important role in maintaining DNA integrity, providing protection against cancer-promoting mutations. Dysfunction of p53 is observed in almost every cancer, with 50% of cases bearing loss-of-function mutations/deletions in the TP53 gene. In the remaining 50% of cases the overexpression of HDM2 (mouse double minute 2, human homolog) protein, which is a natural inhibitor of p53, is the most common way of keeping p53 inactive. Disruption of HDM2-p53 interaction with the use of HDM2 antagonists leads to the release of p53 and expression of its target genes, engaged in the induction of cell cycle arrest, DNA repair, senescence, and apoptosis. The induction of apoptosis, however, is restricted to only a handful of p53wt cells, and, generally, cancer cells treated with HDM2 antagonists are not efficiently eliminated. For this reason, HDM2 antagonists were tested in combinations with multiple other therapeutics in a search for synergy that would enhance the cancer eradication. This manuscript aims at reviewing the recent progress in developing strategies of combined cancer treatment with the use of HDM2 antagonists.

Επίδραση μερικής και ολικής καταστολής του διμερούς ARF-μονοπατιού απόκρισης στις δικλωνικές θραύσεις του DNA στην εξέλιξη του καρκίνου

The DNA damage response (DDR) pathway and ARF function act as barriers of human cancer development. It has been considered that the DDR and ARF exert this function independently of each other. However, a few studies propose that ARF’s activity is positively regulated by the DDR pathway. Examining this hypothesis we performed a series of experiments using molecular techniques such as immunoblotting, immunohistochemistry, immunofluorescence, immunoprecipitation, Real Time Reverse Transcritpion polymerase chain reaction (RT-PCR) in biological material from cell culture or histological samples, as well as ectopic protein expression through plasmid transfections, proteomic analyses, ribosome RNA biogenesis assay and xenografts of human cancer cells. We surprisingly found that ATM suppressed, in a transcription-independent manner, ARF protein levels and activity. Specifically, ATM activated protein phosphatase 1 (PP1). PP1 antagonized Nek2-dependent phosphorylation of nucleophosmin (NPM), liberating ARF from NPM and rendering it susceptible to degradation by the ULF E3-ubiquitin ligase. In human clinical samples, loss of ATM expression correlated with increased ARF levels and in xenograft and tissue culture models, inhibition of ATM stimulated the tumour-suppressive effects of ARF. The importance of the proposed mechanism can be exploited through a therapeutic approach, especially in cases of tumours bearing loss of p53. In such tumours, DDR may act in favour of the tumour cells, since the major effector of the antiumour barriers of apoptosis and senescence is absent, but ATM inhbition could boost ARF’s tumour-suppressive function, contributing to an anti-tumour response.

Power Losses Identification on Turbocharger Hydrodynamic Bearing Systems: Test and Prediction

Design of automotive engines, with increasing focus on downsizing, high performance and low fuel emissions, provides several challenges to turbocharging technology and design. The development of a low friction rotor-bearing system is fundamental to effectively differentiate in the current environment. The exhaust gas energy from the turbine is transmitted through the bearing system to the compressor stage, and then to the engine. A lower bearing system friction allows more power to be transmitted to the compressor. This paper deals with experimental and analytical investigations for rotor-bearing system (RBS) power losses. A powerful test facility and associated experimental approach, based on the temperature drop of the gas flowing through the turbine stage, have been developed. The uncertainty due to instrumentation and process is identified as lower than 12%. The power loss related to the radial bearing is calculated analytically using the laminar Couette model; the power loss due to the axial bearing is calculated by the integration of the 2D Reynolds equation. The additional power loss between the slender shaft and inner bearing surface is calculated using a turbulent Couette model. The power loss due to the seals is not taken into account. Extensive testing in steady state condition has been completed on the test bench. Two different bearing designs with axial grooves have been tested. The influence of oil on the bearing loss has been identified by testing at two oil inlet temperatures (30 °C and 100 °C) and two oil inlet pressures (2 bars and 4 bars). The measurement and prediction of power losses are in good agreement.

Modeling and Experimental Evaluation on Torque Loss in Turbine Test Rig

To evaluate the performance of a turbine through turbine rig test, torque or power generated from the test turbine should be measured. This is measured from a dynamometer or torquesensor installed in the test rig. So, to evaluate the performance of turbine with high precision, the accurate measurement of power or torque is necessary. However, there is an intrinsic difficulty as not all the power generated by the turbine is measured by the dynamometer or torquesensor. A small portion of power generated from test turbine is dissipated through bearing loss and windage loss. This dissipated energy is called mechanical loss of test rig. Therefore, it is necessary to measure the mechanical loss of the test rig for the accurate evaluation of the turbine performance. This paper divides mechanical loss as bearing loss, disk windage loss and extra windage loss. Spin down tests are performed in a 1-stage axial turbine test rig to evaluate each losses. It is found that the dominant loss is bearing loss and the total mechanical loss amounts to 0.78∼1.4% of energy generated at the turbine. And the effect of bearing temperature is investigated and it is found that the mechanical loss is dependent on the bearing temperature and that it increases with decreasing bearing temperature.

Development of High Performance Multi-Lobe Fluid Dynamic Bearings Using a Sintered Material

Recently, in spindle motors for hard disk drive (HDD) devices, fluid dynamic bearings (FDB) with herringbone grooves have come to be used instead of ball bearings due to the demand for high density recording of the devices, improvement in the speed of data transfer, and the quietness of the motor. In this study, a 5-lobe bearing with high bearing stiffness using a sintered material, as a new trial, was developed, and the bearing performance was examined by simulated calculations and experiments. As a result, it was clarified that the 5-lobe bearing had the required performance for practical use in the spindle motor for HDD by means of optimizing the bearing’s dimensions. In addition, bearing loss of the 5-lobe bearing is lower than that of the herringbone bearing, and the 5-lobe bearing showed clearly that it is effective in being used in the miniaturization of HDD spindle motors.