Search

Objective: Iron element has critical roles such as myelin synthesis and neurotransmitter synthesis. Critical enzymes and proteins strictly control iron metabolism. Alterations in the enzyme activities could modify iron metabolism. Metabolic and endocrine changes may influence iron turnover in patients with major depression and anxiety disorders. Materials and Methods: 30 patients with major depressive disorder (MDD), 30 with anxiety disorders (ADs) according to the DSM 5 criteria, and 30 healthy controls were included. Hamilton Depression and Anxiety Scales were the clinical evaluation tools. Blood samples were collected 12 hours of fasting. Hepcidin and Ferroportin levels were measured with ELISA method. Results: Both Hepcidin and Ferroportin levels were lower in the MDD group compared to the ADs group, Hepcidin levels were found to be statistically significantly lower (p= 0.014). In addition, an inverse correlation was observed between the Hamilton Depression Scale score and Ferroportin levels (r= -0.214, p

Rattling is a perennial gear noise problem observed in various powertrain components ranging from manual transmissions to engine balancers and timing gear trains. Under lightly loaded conditions, gear systems that are subjected to input and/or output torque fluctuations exhibit vibro-impacts as tooth separations and coast-side contacts take place in the presence of backlash. Experimental set-ups that can impose tightly controlled torque fluctuations to single or multi-mesh gear train are used here to determine the sensitivity of the rattling noise levels to the magnitudes of backlash within wide ranges of torque fluctuation parameters. Torsional discrete models of the experimental set-ups were used to simulate these rattling motions and to predict impact velocity-based rattle severity indexes as a function of both excitation parameters and backlash magnitudes. Single-mesh results show that the larger backlash values result in higher noise levels in most of the cases. In case of double-mesh systems, the resultant noise levels and the corresponding rattle indices exhibit different sensitivities to backlash magnitudes depending on the excitation conditions.

Biofilm-associated infections cause important health problems all over the world. Because of the resistance to antimicrobials and their possible side effects, researchers' attention has been focused on plant extracts and their components. The aim of this study is to evaluate the antimicrobial and antibiofilm potentials of Salvia microstegia Boiss. et Bal. mericarps. The antimicrobial activity of ethanolic extract obtained from the mericarps was evaluated using the microdilution method against seven standard bacteria and three standard yeast strains. In addition, the effect of the extract on inhibiting biofilm formation and preformed biofilm of Pseudomonas aeruginosa was determined using the crystal violet method. The used extract showed moderate to low antimicrobial activity against tested bacteria and yeasts with minimum inhibitory concentration (MIC) values ranging from 62.5 to 250 µg/mL. Moreover, the extract's potential to inhibit preformed biofilms was found to be greater compared to its potential to inhibit biofilm formation. In conclusion, the tested extract obtained from Salvia microstegia mericarps showed antibiofilm potential, however, additional studies involving different strains are needed to reveal its antimicrobial potential in a more holistic perspective.

The power loss of bearings is a significant factor in the overall efficiency in a drive unit system. Such bearings are subject to combined radial and axial loading needed to support the gear mesh forces. An experimental methodology has been developed to perform sets of power loss measurements on TRB, 4PCBB and DGBB. These measurements were performed under a variety of speed, load, temperature, and lubrication conditions. The loss behaviors of these types of the bearings are discussed, along with the tradeoff of different bearing arrangements for the fuel economy cycles. Several power loss models are employed to assess the accuracy of the estimations as compared to the experimental measurements. At low speed some models showed good correlations for TRB and DGBB, while at higher speed, they start deviating from the testing results. A higher fidelity model for estimating the losses at high speed, especially speed around 20krpm and beyond, needs to be developed. For 4PCBB, the models showed under prediction for the losses within the testing range.

Objective: The aim of this study was to examine the in vivo wound healing potential of Salvia huberi Hedge (endemic to Turkey) on excision and incision wound models in diabetic rats. Method: Male Wistar albino rats, 3-4 months old and weighing 180-240g were used. The animals were randomly divided into five groups including Control, Vehicle and Fito reference, and two different concentrations (0.5% and 1% weight/weight (w/w)) of ethanol extract of Salvia huberi were investigated in both wound models on streptozocin-induced diabetic rats using macroscopic, biomechanical, biochemical, histopathological, genotoxic and gene expression methods over both seven and 14 days. Fito cream (Tripharma Drug Industry and Trade Inc., Turkey) was used as the reference drug. Results: A total of 60 rats were used in this study. Salvia huberi ointments at 0.5% and 1% (w/w) concentrations and Fito cream showed 99.3%, 99.4% and 99.1% contraction for excision wounds, and 99.9%, 97.0% and 99% contraction for incision wounds, respectively. In Salvia huberi ointments and Fito cream groups, re-epithelialisation increased dramatically by both day 7 and day 14 (p Conclusion: The study showed that application of Salvia huberi ointments ameliorated the healing process in diabetic rats with excisional and incisional wounds and may serve as a potent healing agent.

In this study, an experimental methodology is presented for measuring power losses of rolling element bearings under combined radial and axial loading conditions. The set-up developed for this purp...

The phytochemical contents of Salvia virgata mericarps and the antioxidant and antimicrobial activities of its ethanol extract were studied for the first time. S. virgata mericarps were collected in the province of Trabzon, Turkey. Chemical analyses were performed using chromatographic methods. The total phenolic and flavonoid contents and antioxidant potential were measured using Folin-Ciocalteu, Al(NO3)3, and DPPH radical scavenging activity methods, respectively. The antimicrobial activity was evaluated using the microdilution method for all the tested bacterial and fungal strains, with the exception of Mycobacterium tuberculosis for which the resazurin microtiter plate method was applied. The mericarps were rich in glutamic acid (3934 mg/100 g), potassium (12578.8 ?g/g), calcium (12092.0 ?g/g), and dietary fibers (35.565 g/100 g). The total phenolic and flavonoid contents were 2.50 ?g GAE/mg extract and 0.34 ?g QE/mg extract, respectively. The most effective DPPH free radical scavenging activity determined for the highest applied concentration was 92.44%. The ethanol extract obtained from the mericarps was found to be as effective as the reference drug ampicillin (MIC value = 125 ?g/mL) against the nosocomial pathogen Acinetobacter baumannii. In conclusion, S. virgata mericarps provide good nutritional value with low amounts of carbohydrates and high dietary fibers, amino acids, minerals and total phenolic and flavonoid contents and medicinal properties.

Gear tooth bending fatigue failures are instantaneously catastrophic to gear drive power transmission systems. For this reason, gear designers must understand the limits of their design with respect to the desired application and service time. Fatigue testing on gear specimens has been preferred metric on which to base future designs. Single Tooth Bending test (STB) or a Rotating Gear (RG) test methodologies have been used for this purpose. STB type tests generally form the large majority of gear fatigue testing due to cost and availability but does not fully simulate the actual operating conditions of rotating gears in service. As RG evaluations are costly and time-consuming, it is desirable to quantify how a stress-life (SN) relationship regressed through STB testing compares to that produced in RG testing. In this study, both STB and RG test methodologies are employed to test the same specimen design. Matrices of fatigue tests are executed and statistical regression techniques are used to estimate bending fatigue lives as a function of stress for both sets of data. The resultant SN curves are compared to determine any differences in allowable stress. Techniques are then employed using single set data (STBF or RG individually) to demonstrate the calculation of correlation coefficients, which can approximate the total difference determined between the two data sets.

In general, gear mechanical loss is associated with the friction of the lubricating contact surface of the gear and bearing that transmit the power, and a no-load spin loss which is load independent occurs due to gear rotation and the interaction of the bearing component with the lubricating element. In order to minimize planetary gear loss, it is desirable to design by checking the efficiency at the concept design stage. However, a design technique that considers the noise and efficiency of a planetary gear set simultaneously has not been achieved so far. In this paper, a program called 'pRMC with EHL' to check together the efficiency and noise that affected by gear specifications has been developed. By using developed program, planetary gear sets specifications have been designed. And through the experimental evaluation, automatic transmission efficiency could be reduced by 0.3% in combination fuel consumption mode and the planetary gear vibration could be also reduced by 10 dB than former design. Through this designing verification and input parameter correlation, a new planetary gear set designing process has been come up with successfully at the concept design stage.

Gear induced noise represents a major part of overall automotive drivetrain noise. Gear rattle noise is caused by strongly nonlinear dynamic behavior of the gear pair, primarily due to external torque of speed fluctuations under lightly loaded conditions. Such loading conditions cannot be generated by using the conventional gear dynamics test set-ups that employ power recirculating gearbox arrangements or conventional electric motors. In this paper, a new test set-up is introduced to emulate the actual torque/velocity fluctuations of the input and/or output members of a gear train through three-phase synchronous servo-motors. In addition to establishing backlash boundaries, a pair of absolute encoders are used to measure the relative motions of the gears as well as their impacts along the drive and coast sides flanks or gears. Torsional vibratory behavior of a gear pair is presented at different backlash values under several input/output fluctuation conditions along with the companion sound pressure measurements.

External fluctuation torques acting on gear trains having clearances often cause vibro-impact motions with resultant rattle noise issues. In this study, an impact velocity-based rattle severity parameter that correlates with the resultant rattling noise is proposed for multimesh gear trains. An experimental setup is employed to measure torsional vibro-impact motions and the corresponding sound pressure levels of a three-axis gear train under various torque fluctuation conditions. A discrete torsional model of the experimental setup is developed and validated through comparisons to the vibration measurements. An impact velocity-based rattle severity index defined from the predicted response is proposed and shown to correlate well with the measured rattle noise sound pressure levels within a wide range of operating conditions. The demonstrated ability of the proposed rattle severity index in tracking rattle noise allows for the assessment of rattle consequences of a multimesh drivetrain solely from its predicted torsional response.

Background/aim The aim of present study was to investigate the dynamic thiol/disulfide homeostasis as oxidative stress marker in diabetic ketoacidosis (DKA). Materials and methods A total of 77 participants consisting of 32 patients with DKA and 45 healthy volunteers were included in the study. Thiol/disulfide homeostasis (TDH) [total thiol-native thiol/disulfide changes] were measured in both groups (patient group and control group) using a brand new method developed by Erel and Neselioglu. Half of the difference between total thiol and native thiol concentrations gives the amount of disulfide bond. Results Total thiol, native thiol, and disulfide levels in blood were found to be low. The levels of total thiol (P < 0.001) and native thiol (P < 0.001 ) were significantly lower in patients with DKA than in the control group. At the same time, the level of disulfide was nonsignificantly lower in the patient group than the control group (P = 0.388). The level of IMA was higher in the patient group than in the control group (P < 0.001). Conclusion The total thiol, native thiol, and disulfide levels in DKA decrease in favor of oxidative stress.

The fatty acid, sterol, and tocol compositions, mineral, total phenolic, and flavonoid contents, and antioxidant and antimicrobial activities of Salvia longipedicellata Hedge (endemic) mericarps were examined for the first time. Mericarps were rich in α-linolenic acid (47.72%), β-sitosterol (54.46%), γ-tocopherol (375.68 mg/kg), and potassium (75.411 μg/g). Total phenolic and flavonoid contents were 1.04 μg GAE/mg extract and 0.32 μg QE/mg extract, respectively. The antioxidant and antimicrobial potential of mericarps were also determined.

In this study, a rough surface thermal elastohydrodynamic lubrication (TEHL) model tailored for the simulation of high-speed and high-temperature contacts of relatively smooth surfaces is introduce...

This article describes the development of a high-speed, two-disc tribometer to conduct traction and scuffing tests emulating typical aerospace and automotive gear contacts. This tribometer is capab...

Dynamic response of a gear pair subjected to input and output torque or velocity fluctuations is examined analytically. Such motions are commonly observed in various powertrain systems and identified as gear rattle or hammering motions with severe noise and durability consequences. A reduced-order torsional model is proposed along with a computationally efficient piecewise-linear solution methodology to characterize the system response including its sensitivity to excitation parameters. Validity of the proposed model is established through comparisons of its predictions to measurements from a gear rattle experimental setup. A wide array of nonlinear behavior is demonstrated through presentation of periodic and chaotic responses in the forms of phase plots, Poincaré maps, and bifurcation diagrams. The severity of the resultant impacts on the noise outcome is also assessed through a rattle severity index defined by using the impact velocities.

Vibro-impacts are common in various automotive engine and transmission gear applications. They are known to cause excessive noise levels, often called rattling or hammering. Input and output fluctuations acting on such systems cause tooth separations and sequences of impacts allowed by backlash at the gear mesh interfaces. The fluctuations leading gear rattling have often been studied for specific applications with the excitations produced typically by an internal combustion engine. As such, rattle evaluations have been often empirical and specific to the systems considered. In this study, an experimental test setup of a gear pair is developed to emulate the same torque fluctuations in a laboratory environment. This setup is used to establish an impact velocity-based rattle severity index defined by the measured torsional behavior of the drive train that is shown to correlate well with the measured sound pressure levels. With that, a validated dynamic model of the experimental setup is employed to predict the same index to allow estimation of rattle noise outcome solely from a torsional dynamic model of the drivetrain. Predicted rattle severity indexes are shown to agree well with the measured ones within wide ranges of torque fluctuations and backlash magnitudes, allowing an assessment of rattle performance of a drivetrain solely from a torsional model.

Aim: To determine the antiproliferative and cytotoxic activities of Geranium and Erodium species against human cancer and noncancer cell lines, respectively. Methods: Twenty-one species of Geranium and Erodium were extracted and screened against cancerous and noncancerous human cell lines. Results: In a dose-response manner, G. glaberrimum, G. asphodeloides, E. brandianum and E. leucanthum were able, with variable potency, to inhibit cellular proliferation. Except for E. brandianum, all extracts induced cellular autophagy in tumor cells with similar levels to that of rapamycin; but, only E. brandianum induced cellular apoptosis, likely through Bcl2 and BAX protein expressions. Discussion: This is the first study to report the potential antiproliferative effects of ethanol extracts of several Geraniaceae species., Lay abstract Several plant species of the genera Geranium and Erodium were extracted and screened against five tumor cell lines for their potential antitumor activities. Out of the tested species, four showed potential antitumor action against all the tumor cells used. Interestingly, they appeared to achieve their antitumor activities by inducing important cellular defense mechanisms called autophagy and apoptosis. The current work is the first to test the antiproliferative potential of these species against different tumor cells.

BACKGROUND/AIM Permanent daylight saving time has been implemented in Turkey since 2016. The present study determines the characteristics of road traffic collisions in the short-term, trauma severity, and whether permanent daylight saving time has an impact on these parameters. MATERIALS AND METHODS Drivers admitted because of road traffic collisions to a tertiary care university hospital emergency service two weeks before and after the transition to wintertime in 2014 and 2015 and summertime in 2015 and 2016 as well as those admitted two weeks before and after the same period with permanent daylight saving time in 2016 and 2017 wintertime and 2017 and 2018 summertime were included in the study. Trauma severity was measured using the Injury Severity Score. RESULTS The study analysed the data of 710 patients. There was no statistically significant difference was found between admissions in the summertime and permanent daylight saving time periods in terms of gender, time of admission, week of admission, Injury Severity Score and outcome (P > .05 for all values). CONCLUSIONS In this study, we examined the short-term effects of daylight saving time on road traffic collisions, and demonstrated that it had no impact on the number or time of admission, trauma severity and patient outcomes. More comprehensive studies covering longer periods can be performed across the country.

A tribo-dynamic model of ball bearings is proposed to predict their load-dependent (mechanical) power losses. The model combines (i) a transient, point contact mixed elastohydrodynamic lubrication (EHL) formulation to simulate the mechanics of the load carrying lubricated ball-race interfaces and (ii) a singularity-free dynamics model and establishes the two-way coupling between them that dictates power losses. The dynamic model uses a vectoral formulation with Euler parameters. The EHL model is capable of capturing two-dimensional contact kinematics, velocity variations across the contact as well as asperity interactions of rough contact surfaces. Resultant contact surface shear distributions are processed to predict mechanical power losses of example ball bearings operating under combined radial and axial forces. An experimental setup is introduced for measurement of the power losses of rolling-element bearings. Sets of measurements taken by using the same example ball bearings are compared with those predicted by the model to assess its accuracy in predicting mechanical power loss of a ball bearing within wide ranges of axial and radial forces.

The pollen grains of 19 Turkish Salvia species in Aethiopis, Drymosphace, Hemisphace, Hymenosphace and Salvia sections, 13 of which are endemic to Turkey, were investigated, documented and illustrated through Light Microscopy (LM) and Scanning Electron Microscopy (SEM). This study provides pollen data of 14 species for the first time. The pollen grains of the species examined are monads, isopolar, radially symmetrical and hexacolpate, mostly medium in size, slightly elliptic to more or less circular in polar view and mainly oblate-spheroidal in equatorial view. Two different ornamentation types are recognized on exine sculpturing; reticulate-perforate and bireticulate. The present results do not generally support the traditional infrageneric classification of Salvia, but provide useful pollen characters for species delimitation.

Leucojum aestivum (snowflake) contains galantamine, a medication used for the treatment of Alzheimer's disease. However, polyphenolic compounds of this species were not studied earlier. Proper understanding of the polyphenolics in the species and their antioxidant properties may lead to a review of their medical use. Therefore, in this study, the polyphenolic content of L. aestivum was determined by UV spectrophotometric and HPLC methods. DPPH, ABTS+, and RPC assays were performed for assessment of its antioxidant potential. Flower and leaf extracts of L. aestivum were found to have more antioxidant activity than its bulbs. This result demonstrated that it was an important source of antioxidant compounds. Qualitative and quantitative findings showed that it contained significant amounts of polyphenols. Naringenin, rosmarinic, pcoumaric, syringic, and gallic acid compounds were identified in the leaf and flower extracts. Methanol extracts of the fowers, leaves and bulbs had no activity against pathogenic bacterial strains. The methanolic flower and leaf extracts showed the most antifungal effective against Alternaria citri. Moreover, they were found to be a slightly antifungal effective against Penicillium glabrum and Cladosporium cladosporioides. Anatomical studies were performed on leaf transverse and surface sections of L. aestivum and its bulb cross-section. The isobilateral leaf had tetracytic type of stomata. The mesophyll comprised arge lysigenous cavities and contained crystalline inclusions (raphide crystals). Large amounts of compound starch grains were recognized to occur in parenchyma cells in the bulb. SEM observations revealed that leaf epidermal cells had conspicuous boundaries and their membranes on periclinal walls were striate. © 2019 Academic Press. This study is a part of the M.Sc. dissertation of the first author at Department of Molecular Biology and Genetics at the Institute of Natural and Applied Sciences, Usak University, Usak, Turkey. We thank Prof. Dr. Safiye Elif Korcan at Usak University for her help in antimicrobial and antifungal studies.

Salvia L., the largest genus of the family Lamiaceae, is composed of many well-known plants of medicinal value. This study provides the first data on micromorphology, myxocarpy, mineral content and in vitro antimicrobial and antiproliferative activities of mericarps of Salvia pilifera, considered to be a vulnerable endemic species from Turkey. The macro-and micromorphological mericarp traits were documented and illustrated via stereo microscopy and scanning electron microscopy. Mineral content of mericarps was analyzed using ICP-MS. Ethanol extract of mericarps was tested against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Acinetobacter baumannii, Aeromonas hydrophila, Candida albicans, Candida tropicalis, and Candida glabrata using broth microdilution method. Antimycobacterial activity was performed against Mycobacterium tuberculosis H37Rv using resazurin microtiter plate method. Ampicillin, Ethambutol, Isoniazid, and Fluconazole were chosen as reference drugs. Antiproliferative effect of the extract was tested against A549 human lung cancer cell lines using MTT test. The size of the mericarps was 4.38±0.17 mm in length and 3.28±0.13 mm in width. The general shape was elliptic to widely elliptic. The abscission scar was nearly rounded. The ornamentation pattern of the surface was colliculate with polygonal exocarp cells. Myxocarpy was observed on the surface of the mericarps when they become hydrated. Transparent mucilaginous cells showed a moderate reaction with extensions more than 0.1 mm long. Potassium and calcium were determined as major minerals (80.662±0.234 and 41.892±0.399 µg/g, respectively). The extract showed greater antibacterial activity against A. baumannii compared to Ampicillin (62.5 and 125 µg/mL MIC values, respectively). Cell viability level of the extract (100 ?g/mL) was found to be statistically lower than control group against A549 human lung cancer cell lines (P

© 2021 Phytochemical Society of EuropeThe anti-gout effect of Erodium birandianum Ilarslan & Yurdak. was investigated through xanthine oxidase (XO) inhibition using in vitro and in silico experiments. The ethanol extract of E. birandianum (EB) with 82.26 ± 0.10 % of XO inhibitory activity at 100 μg/mL was sequentially fractionated. The extract and active fractions were analyzed using LC-Q-ToF-MS. Gallic, caffeic, quinic, and syringic acids, catechin, epicatechin, rutin, luteolin, apigenin, and quercetin were detected in the extract and active subfractions. In the active subfractions, presence of procyanidin derivatives having molecular weight over 850 was demonstrated through LC-Q-ToF-MS library. Catechin, caffeic acid, rutin, and quercetin were tested against XO, and the highest inhibition was caused by quercetin (98.03 ± 2.34 %). XO inhibitory effect of gallic acid, caffeic acid, catechin, epicatechin, luteolin, apigenin, and quercetin was investigated by molecular docking experiments. Probability of their XO inhibition was estimated using PASS and Swiss Target Prediction programs. Possible toxicities were estimated by VEGA QSAR Mutagenity, CONSENSUS, ToxTREE SAR, and VEGA hepatotoxicity models. Quercetin as well as luteolin, apigenin, and gallic acid were deduced to be most likely responsible for the marked XO inhibitory effect of EB extract and active subfractions.

In the current work, the ethanol extracts of (36 samples from various locations) 21 species of Geranium were investigated for their tyrosinase (TYR) inhibitory and antioxidant activity. G. glaberrimum (GG) (31.41 +/- 1.11 %), G. macrostylum (31.15 +/- 1.35 %), and G. lasiopus (30.01 +/- 0.09 %) had the highest inhibition against TYR, which were proceeded to further phytochemical analyses. The major compounds were gallic and ellagic acids. G. glaberrimum Boiss. & Heldr. were further fractioned by preparative-LC, in which the second fraction (GG-2) resulted in the highest inhibition, which was analyzed by LC-MS-MS. Geraniin and corilagin in GG-2 and quinic acid, gallic acid, 3,4-dihydroxy benzoic acid, 4-O-methyl gallate, geraniin, corilagin, ellagic acid, and quercetin were shown to be present in GG-EtOH extract. Quercetin (IC50 = 54.11 +/- 1.92 mu g/mL) was the most active inhibitor. Molecular interactions of the compounds with TYR were examined. Structure-activity relationship was achieved by PASS and Swiss Target Prediction programs. Ellagic acid and quercetin also displayed good molecular connections with the active site of TYR through pi-pi interactions and binding with two Cu atoms at the center of the enzyme. Thus, these two compounds appeared to be the most promising TYR inhibitors approved by both in vitro and in silico results.

Filistinliler ve Yahudiler arasındaki çatışma Ortadoğu’da yaşanan sosyal, siyasal ve ekonomik sorunlarının birçoğunu etkileyen bir ihtilaftır. İlk Yahudi yerleşimcilerin Filistinlilerle karşılaşması, Ortadoğu’daki birçok güvenlik sorunuyla bağlantılıdır. Bu kitabı daha önceki araştırmalardan farklı kılan, Filistin-İsrail çatışmasını klasik güvenlik yaklaşımlarına üzerinden değil toplumsal güvenlik kavramsallaştırması bağlamında disiplinlerarası bir bakış açısıyla incelemesidir. Bu bağlamda kitabın odak noktası; aktör olarak devletlerden ziyade Yahudi ve Filistinli üst kimliğindeki topluluklardır. Eser çatışmaların materyal ve askeri yönlerinin yanı sıra toplum ve insanla bağlantılı olan kimliksel, bilişsel ve duygusal yönlerinin analizlere dahil edilmesini teklif eder.

In this study, an experimental methodology is presented to separate various components of the power loss of a gearbox. The methodology relies on two separate measurements. One is designed to measure total power loss of a gearbox housing a single spur gear pair under both loaded and unloaded conditions such that load-independent (spin) and load-dependent (mechanical) components can be separated. With the assumption that gear pair and rolling element bearings constitute the bulk of the gearbox power loss, a second measurement system designed to quantify rolling element bearing losses is proposed. With this setup, spin and mechanical power losses of rolling element bearings used in the gearbox experiments are measured. Combining the sets of gearbox and bearing data, power loss components attributable to the gear pair and rolling element bearings are quantified as a function of speed and torque. The results indicate that all gear and bearing related components are significant and a methodology such as the one proposed in this study is warranted.

In this study, a non-Newtonian, transient, isothermal, mixed elastohydrodynamic lubrication (EHL) model is proposed for helical gear contacts. The model accounts for nonelliptical contacts subject to spatially varying sliding and rolling velocity fields that are not aligned with any principal axis of the contact region, which is the case for helical gear contacts. The time-varying changes pertaining to key contact parameters and relative motion of roughness profiles on mating tooth surfaces are captured simultaneously to follow the contact from the root to the tip of a tooth while accounting for the transient effect due to relative motions of the roughness profiles. Actual tooth load distributions, contact kinematics, and compliances of helical gear contacts are provided to this model by an existing helical gear load distribution model. Measured three-dimensional roughness profiles covering the entire meshing zone are incorporated in the analyses to investigate its impact on the EHL conditions as well as mechanical power loss. Results of a parametric sensitivity study are presented to demonstrate the influence of operating conditions and surface roughness on the EHL behavior and the resultant gear mesh mechanical power loss of an example helical gear pair. The accuracy of the proposed mixed-EHL model is assessed by comparing the mechanical power loss predictions to available experimental results.

The quasi-static behaviors of a double-helical gear pair is investigated both experimentally and theoretically with the main focus on the influence of the key design and manufacturing parameters associated with double-helical gears, including nominal right-to-left stagger angle, the stagger angle deviation (error) from the nominal stagger angle, and axial gear supporting conditions. On the experimental side, a double-helical gear test setup proposed earlier (Kang, M. R., and Kahraman, A., 2015, “An Experimental and Theoretical Study of Dynamic Behavior of Double-Helical Gear Sets,” J. Sound Vib., 350, pp. 11–29). for studying dynamics of the same system is employed that allows adjustable right-to-left stagger angles, intentional stagger errors, and axial support conditions. Specific measurement systems are developed and implemented simultaneously to measure the static motion transmission error and axial motions of the gears under low-speed conditions, as well as gear root strains to determine right-to-left load-sharing factors. A test matrix that covers wide ranges of stagger angles, intentional stagger error, and axial support conditions is executed within a range of torque transmitted to establish an extensive database. On the modeling side, the measured quasi-static behavior of double-helical gear pairs is simulated by using an existing quasi-static double-helical load distribution model (Thomas, J., and Houser, D. R., 1992, “A Procedure for Predicting the Load Distribution and Transmission Error Characteristics of Double Helical Gears,” World Congress-Gear and Power Transmission, The 3rd World Congress—Gear and Power Transmission, Paris.). Direct comparison of the measurements and predictions of loaded static transmission error, axial play, root stresses, and right-to-left load-sharing factors are used to validate the quasi-static model as well as describing the measured behavior.

High-cycle gear tooth bending fatigue lives of spur gears under fully reversed and fully released loading conditions are compared in this experimental study. The experimental methodology described in an earlier publication, (Hong et al. 2020, “A Rotating Gear Test Methodology for Evaluation of High-Cycle Tooth Bending Fatigue Lives Under Fully Reversed and Fully Released Loading Conditions,” Int. J. Fatigue, 133, p. 105432. 10.1016/j.ijfatigue.2019.105432), is employed to perform two sets of rotating, gear tooth bending fatigue tests. Statistical analyses are performed to regress stress versus life (S–N) curves under both loading conditions. These curves indicate that a gear under fully reversed loads has a shorter bending life at the same maximum tooth root stress as a gear under fully released loads. Various planetary gear set kinematic conditions with different stationary members are considered to determine the equivalent number of tooth loading cycles per revolution of the sun gear. They are combined with established S–N curves under both loading conditions to determine the ratios of allowable maximum tooth root stresses amongst the gear components of a P-planet gear set such that each gear in the set has the same bending fatigue life. A “stress-balanced” gear set designed to these stress ratios is expected to have the same bending fatigue life for its sun, ring, and planet gears, ensuring that the planetary gear set life is the longest.