scholarly journals MODIFICATIONS OF GEAR WHEEL TEETH OF AVIATION GEARBOXES TO INCREASE THEIR OPERATIONAL RELIABILITY AND TECHNOLOGY

2021 ◽  
pp. 112-125
Author(s):  
O. Pilipenko ◽  
D. Kolesnik ◽  
A. Berezniak ◽  
R. Kholodnyi
Keyword(s):  
Contact Zone ◽  
Gear Wheel ◽  
Operational Reliability ◽  
Spur Gears ◽  
Operational Characteristics ◽  
Significant Difference ◽  
Different Types ◽  
Gear Wheels ◽  
Gear Drives ◽  
Radical Type

The types and methods of modifications of teeth and gear wheels, which have found application in gearboxes of aircraft and helicopters, are presented. Features of geometry, parameters of different types of initial produced contours, their modifications, application and influence of various factors on improving the operational characteristics of gear drives of aviation gearboxes are considered. Arcuate (short and long) and short linear options for modifying the tooth profiles of aircraft gearboxes are best suited to absorb the errors of spur gears. There was no significant difference in the use of short and long correction for a relative decrease in temperature in the contact zone of the wheel teeth, therefore, the use of any correction of the tooth profile, with rare exceptions, turns out to be useful. The advantages of using increased profile angles in comparison with the standard ones used in general mechanical engineering are considered. Development of designs of teeth and gear wheels in aircraft gearboxes, the use of gears with teeth of an asymmetric profile, which can be considered as a cardinal modification of the tooth profiles. The use of such gears increases the strength of the teeth due to the increase in the thickness of the teeth. Unsymmetrical teeth have a large thickness at the tip, which reduces teeth chipping and due to their greater height, greater smoothness of engagement is achieved, bending and contact stresses are reduced. The most radical type of modification is the use of asymmetric profiles of the teeth of the wheels of aircraft gearboxes.

scholarly journals Constructional design of the body shape of large gear wheels

2021 ◽  
Vol 1199 (1) ◽  
pp. 012019
Author(s):  
S Sivák ◽  
S Maláková
Keyword(s):  
Body Shape ◽  
Gear Wheel ◽  
The Body ◽  
Spur Gears ◽  
Performance Parameters ◽  
Large Gear ◽  
The Subject ◽  
Body Shapes ◽  
Gear Wheels ◽  
Means Of Production

Abstract The development of modern machines and means of production is characterized by ever-increasing performance parameters with decreasing equipment weight. When designing large gears, it is also necessary to consider the influence of the body shape of the gear wheel. The body shape of gear wheel must meet the basic requirements of stiffness and strength with the lightest possible construction of the gear wheel body. The work is focused on large gears, made with relief. Such gears can be forged, cast, or made by welding. The shape of the gear wheel body depends on several factors such as the size of the wheel, the material, the method of manufacture or use. The paper provides an overview of the body shapes used by large spur gears. These body shapes of spur gears will be the subject of further research, where suitability will be assessed based on stiffness of teeth and wheel weight.

scholarly journals DAMAGING AND DESTRUCTION OF REDUCTION TRAINS OF MI-8 HELICPTER AND ITS MODIFICATIONS

2020 ◽  
pp. 92-105
Author(s):  
O. Pilipenko ◽  
D. Kolesnik ◽  
A. Berezniak ◽  
V. Shokha
Keyword(s):  
High Speed ◽  
Fatigue Cracks ◽  
Gear Wheel ◽  
Gear Train ◽  
Gear Teeth ◽  
Operation Conditions ◽  
Different Types ◽  
Negative Effect ◽  
Surface Destruction ◽  
Gear Wheels

The results of quantitative factographic study of the Mi-8 helicopter (its modifications) reduction trains with different types of gear coupling, the destruction of which occurred while in flight due to the presence of preliminary material damage at the stage of production of the gear wheels and during their operational employment are presented in a generalized form. Contact teeth destruction as the main cause of failures of high-speed gear wheels in well-lubricated enclosed gears are considered. The causes of the wearing and sticking of the teeth along their lateral surfaces as well as scoring and destruction depending on the origin of the cracks are revealed. The main causes of damaging and destruction of helicopter reduction trains, locations and origination of fatigue cracks spots are identified. Different types of contact and fatigue destructions due to various reasons are considered. Dynamic loading of gear wheels disks as a result of their rotation damages the material of the wheels in the area of multi-cycle fatigue due to the repeatability of flight load cycles. Lamination or deep contact destruction of the material, which sometimes take place in gears with surface hardened (cemented, tempered, nitrided, etc.) teeth, are much more dangerous than surface destruction of the material since sufficiently large fractions of the hardened material layer are split away from the teeth that can quickly break down an entire gear train. The main causes of contact teeth destruction are load concentration along the length and profile of the teeth, the presence of residual tensile stresses on the working surfaces of the teeth, adverse operational damage to the tooth profiles and negative effect of lubricating fluid on the teeth. For a repaired gear train the cause of the uneven load distribution along the length of the teeth may be the poor assembly of the gear wheels and other transmission parts which leads to unsatisfactory contact of the gear teeth in the assembled unit. The revealed peculiarities of the destruction process indicate regular crack proliferation from flight to flight. According to the operation conditions of the gear wheel, its regular extensive loading refers only to the full cycle of starting and stopping the reducer train or unloading the helicopter in flight, which in this case corresponds to the cycle of helicopter operation in one flight. Therefore, the number of detected fatigue lines corresponds to the number of helicopter flights. To increase the smoothness of gear train running which affects positioning accuracy, reduce wear during running-in, decrease noise, eliminate early jamming, and ultimately, to increase the resource, it is necessary to eliminate the edge interaction of the teeth, which causes their excessive wear.

Households Discrimination in School Enrolment in Pakistan: Does gender matter?

2018 ◽  
Vol 2 (1) ◽  
pp. 29-36
Author(s):  
Ali Muhammad ◽  
Zahoor Ul Haq ◽  
Imad Khan
Keyword(s):  
Low Income ◽  
Gender Discrimination ◽  
Rural Areas ◽  
Gender Disparity ◽  
School Enrollment ◽  
Female Education ◽  
Public And Private ◽  
Significant Difference ◽  
Different Types ◽  
Socio Economic Factors

This study uses Pakistan Social and Living Measurement Survey 2016 to study gender discrimination in school enrollment across the four provinces of Pakistan using bi-variate analysis. Results show that there is highly significant difference between male and female education in rural areas (x^2=4940.50 and p<0.05). Analysis indicate that gender disparity in enrollment is significantly higher in low income households (x^2=115.468 and P<0.05). The study also showed that as compared to male, fewer female are enrolled in both public and private sectors. Hence, socio-economic factors play important role in making decision about children enrollment in different types of school. The study recommends that government to take appropriate steps to reduce gender discrimination in school enrollment by offering subsidy on female education in the country.

Using Histological and Chemical Methods for Detection of Unauthorized Tissues Addition in Emulsion Type Meat Product

2020 ◽  
Keyword(s):  
Vascular Tissue ◽  
Meat Product ◽  
Calcium Content ◽  
Processed Meat ◽  
Low Protein ◽  
Significant Difference ◽  
Different Types ◽  
Plant Stem ◽  
High Level ◽  
Reliable Methods

Total twenty different processed meat plant producing emulsion type sausage were histologically and chemically examined for detection of adulteration with unauthorized tissues. Results revealed that samples were adulterated with different types of animal tissues included; hyaline cartilage, tendon, spongy bone, peripheral nerve trunk, basophilic matrix, lymphatic tissue, fascia, fibrocartilage and vascular tissue. Moreover, these samples were adulterated Also, adulterated with plant tissue included; plant stem, leaves and root. Chemical analysis showed a significant difference in their chemical composition (moisture, fat, protein, ash and calcium) content. Moisture and fat content varied around the permissible limit of E.S.S. while low protein, high ash and calcium content was detected in the examined samples. Therefore, Histological and chemical examinations can be used as reliable methods to detect adultration using unauthorized addition of both animal and plant tissues in processed meat product samples which revealed a high level of falsification.

scholarly journals Snail mucus from the mantle and foot of two land snails, Lissachatina fulica and Hemiplecta distincta, exhibits different protein profile and biological activity

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Nattaphop Noothuan ◽  
Kantamas Apitanyasai ◽  
Somsak Panha ◽  
Anchalee Tassanakajon
Keyword(s):  
Biological Activities ◽  
Protein Pattern ◽  
Protein Profile ◽  
Antibacterial Properties ◽  
Biological Properties ◽  
Specific Protein ◽  
Land Snails ◽  
Snail Species ◽  
Significant Difference ◽  
Different Types

Abstract Objective Snails secrete different types of mucus that serve several functions, and are increasingly being exploited for medical and cosmetic applications. In this study, we explored the protein pattern and compared the biological properties of the mucus secreted from the mantle collar and foot of two snail species, Lissachatina fulica and Hemiplecta distincta. Result Protein profile showed a different pattern between the two species and between the two secretory parts. The mantle-specific protein bands were further characterized and among them was an antibacterial protein, achacin. Accordingly, the mucus from the mantle exhibited the higher antibacterial activity than that from the foot in both snail species. The mucus from H. distincta, first reported here, also showed antibacterial properties, but with a lower activity compared to that for L. fulica. Snail mucus also exhibited anti-tyrosinase activity and antioxidant activity but with no significant difference between the foot and mantle mucus. These results indicate some different protein compositions and biological activities of snail slime from the mantle and foot, which might be associated with their specific functions in the animal and are useful for medical applications.

Analysis of Support for Parents in Raising Children with Dyslexia

2020 ◽  
pp. 0192513X2094892
Author(s):  
Athira Amira Abd Rauf ◽  
Maizatul Akmar Ismail ◽  
Vimala Balakrishnan ◽  
Loh Sau Cheong ◽  
Novia Indriaty Admodisastro ◽  
...  
Keyword(s):  
Marital Status ◽  
Self Esteem ◽  
Peer To Peer ◽  
Government Support ◽  
Anova Analysis ◽  
Raising Children ◽  
The Social ◽  
Significant Difference ◽  
Different Types ◽  
One Way Anova

The parents of children with dyslexia often experience more parenting stress and depressive symptoms compared to other parents. Studies have shown that supporting and encouraging such parents help in reducing their frustrations, fear, anger, and low self-esteem towards their children. The purpose of this study was to identify and examine the different types of support needed by the parents of children with dyslexia and to explore the relationships between the required support with the parents’ marital status. Fifty questionnaires were distributed to the parents of children with dyslexia and analyzed. The findings showed that the type of support needed for parents of children with dyslexia could be grouped into social, peer-to-peer, financial, and government support. Furthermore, the analysis indicated that there were no significant differences between the social (p = 0.4014), peer-to-peer (p = 0.5020), and government (p = 0.7121) support with parents’ marital status. However, based on one-way ANOVA analysis, there was a significant difference found between the parents’ marital status and financial support (p = 0.0241). Accordingly, it is anticipated that the implication of this research could be used as a guide and a reference for supporting and encouraging parents of children with dyslexia and other learning disabilities.

Comparison of two types of inocula during acclimation and stable operation for nitrophenol biodegradation in an anaerobic-aerobic SBR

2006 ◽  
Vol 54 (10) ◽  
pp. 39-45
Author(s):  
A. Vargas ◽  
D. González ◽  
A. Estival ◽  
G. Buitrón
Keyword(s):  
Wastewater Treatment ◽  
Treatment Plant ◽  
The Other ◽  
Stable Operation ◽  
Reaction Phase ◽  
Toxic Compound ◽  
Anaerobic Wastewater Treatment ◽  
Significant Difference ◽  
Different Types ◽  
Batch Bioreactors

This work presents a comparison of two inocula used for the acclimation of two anaerobic-aerobic sequencing batch bioreactors used for toxic wastewater treatment. The bioreactors were acclimated with different types of sludge: one coming from an anaerobic wastewater treatment plant and the other one from a conventional aerobic activated sludge plant. The model toxic compound was p-nitrophenol, which is reduced to p-aminophenol during the initial anaerobic phase of the reaction, and later mineralized during a posterior aerated reaction phase. Biodegradation of the compounds was monitored using UV/Vis spectrophotometry. After acclimation stabilization of the sludge and of the process was also monitored. Results show that there is no significant difference in acclimation times and stability of the process between the two employed inocula, and thus an originally anaerobic inoculum presents no apparent advantage over a more easily accessible aerobic one.

A radiopathological classification of dural tail sign of meningiomas

2012 ◽  
Vol 117 (4) ◽  
pp. 645-653 ◽  
Author(s):  
Song-tao Qi ◽  
Yi Liu ◽  
Jun Pan ◽  
Silky Chotai ◽  
Lu-xiong Fang
Keyword(s):  
Tumor Cells ◽  
Histopathological Examination ◽  
Who Grade ◽  
Simpson Grade ◽  
Mri Studies ◽  
Dural Tail Sign ◽  
Significant Difference ◽  
Different Types ◽  
Dural Tail

Object The completeness of meningioma resection depends on the resection of dura mater invaded by the tumor. The pathological changes of the dura around the tumor can be interpreted by evaluating the dural tail sign (DTS) on MRI studies. The goal of this study was to clarify the pathological characteristics of the DTSs, propose a classification based on the histopathological and radiological correlation, and identify the invasive range of tumor cells in different types of DTS. Methods The authors retrospectively reviewed 179 patients with convexity meningiomas who underwent Simpson Grade I resection. All patients underwent an enhanced MRI examination preoperatively. The convexity meningiomas were dichotomized into various subtypes in accordance with the 2007 WHO classification of tumors of the CNS, and the DTS was identified based on the Goldsher criteria. The range of resection of the involved dura was 3 cm from the base of the tumor, which corresponded with the length of DTS on MRI studies. Histopathological examination of dura at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 cm from the base of the tumor was conducted, and the findings were correlated with the preoperative MRI appearance of the DTS. Results A total of 154 (86%) of 179 convexity meningiomas were classified into WHO Grade I subtype, including transitional (44 [28.6%] of 154), meningothelial (36 [23.4%] of 154), fibrous (23 [14.9%] of 154), psammomatous (22 [14.3%] of 154), secretory (10 [6.5%] of 154), and angiomatous (19 [12.3%] of 154). The other 25 (14%) were non–Grade I (WHO) tumors, including atypical (12 [48%] of 25), anaplastic (5 [20%] of 25), and papillary (8 [32%] of 25). The DTS was classified into 5 types: smooth (16 [8.9%] of 179), nodular (36 [20.1%] of 179), mixed (57 [31.8%] of 179), symmetrical multipolar (15 [8.4%] of 179), and asymmetrical multipolar (55 [30.7%] of 179). There was a significant difference in distribution of DTS type between Grade I and non–Grade I tumors (p = 0.004), whereas the difference was not significant among Grade I tumors (0.841) or among non–Grade I tumors (p = 0.818). All smooth-type DTSs were encountered in Grade I tumors, and the mixed DTS (52 [33.8%] of 154) was the most common type in these tumors. Nodular-type DTS was more commonly seen in non–Grade I tumors (12 [48%] of 25). Tumor invasion was found in 88.3% (158 of 179) of convexity meningiomas, of which the range of invasion in 82.3% (130 of 158) was within 2 cm and that in 94.9% (150 of 158) was within 2.5 cm. The incidence of invasion and the range invaded by tumor cells varied in different types of DTS, and differences were statistically significant (p < 0.001). Conclusions Nodular-type DTS on MRI studies might be associated with non–Grade I tumors. The range of dural resection for convexity meningiomas should be 2.5 cm from the tumor base, and if this extent of resection is not feasible, the type of DTS should be considered. However, for skull base meningiomas, in which mostly Simpson Grade II resection is achieved, the use of this classification should be further validated. The classification of DTS enables the surgeon to predict preoperatively and then to achieve the optimal range of dural resection that might significantly reduce the recurrence rate of meningiomas.

scholarly journals An exertion of enhance milk yield of native Pabna cattle through using different types of calcium salt of fatty acid

2018 ◽  
Vol 15 (2) ◽  
pp. 137-146 ◽  
Author(s):  
D Yeasmin ◽  
N Islam ◽  
NR Sarker ◽  
N Huda ◽  
A Habib ◽  
...  
Keyword(s):  
Body Weight ◽  
Fatty Acid ◽  
Milk Yield ◽  
Calcium Salt ◽  
Bos Indicus ◽  
Mustard Oil ◽  
Initial Body Weight ◽  
Significant Difference ◽  
Different Types ◽  
Concentrate Mixture

Keeping consideration on increasing quality milk production through addition of conventional fat, an experiment accords CRD design was conducted at Bangladesh Livestock Research Institute, Savar, Dhaka for a period of 30 days including 5 days of digestibility trial. Twenty lactating Pabna cattle of average 250.1 ± 13.64 kg (Bos indicus) of initial body weight with average milk yield of 2.88 ± 0.38 kg were selected and divided into four groups randomly having five cows in each. The imposed treatments were T0, T1, T2, and T3; in where To= German grass + Concentrate mixture without Ca salt of fatty acid + 2.5 % DCP, T1= German grass + Concentrate mixture + 2.5 % soybean based Ca salt of fatty acid, T2= German grass + Concentrate mixture + 2.5 % mustard based Ca salt of fatty acid and T3= German grass + Concentrate mixture + 2.5% palm-oil based Ca salt of fatty acid. The result showed that, calcium salt of fatty acid influenced to increase of milk yield significantly among (P<0.001) the treatments; in where highest yield gained in T1 (3.53 kg d-1) followed by T2, T0 and T3 (3.33, 2.44 and 2.24, respectively). Besides this, all other parameters analytically examined in this experiment i.e. intake, apparent digestibility, gained body weight and chemical composition of milk showed non-significant difference among the treatments. From the analytical value and discussion, it may be suggested that, calcium salt of fatty acid formulated from soybean oil or mustard oil could be used for enhancing better quality milk yield.SAARC J. Agri., 15(2): 137-146 (2017)

scholarly journals DIFFERENT APPROACHES OF CLIENTS AND CONSULTANTS TO CONTRACTORS’ QUALIFICATION AND SELECTION

2005 ◽  
Vol 11 (4) ◽  
pp. 267-276 ◽  
Author(s):  
Mehmedali Egemen ◽  
Abdulrezak N. Mohamed
Keyword(s):  
Construction Industry ◽  
Selection Processes ◽  
Significant Difference ◽  
Different Types ◽  
Almost All ◽  
High Willingness

Nowadays, clients are the dominant groups in almost all types of industries. However, the construction industry is unique and consultants, as representatives of clients, are very important figures in this industry as well. By presenting survey findings of 91 clients and 50 consultants, this study reveals clients’ and consultants’ differing expectations of contracting organisations during contractor qualification and selection. The study has clearly confirmed the fact that consultants’ perspectives are rather different and their contractors’ expectations of their clients vary very significantly from the clients themselves. Furthermore, significantly different results were found even among different types of consultants and different categories of clients. Moreover, this study showed that both clients and consultants had high willingness to continue working with the same contractor in possible future works assuming they are satisfied with the previous works. The criteria, which contribute to achieving full client and/or consultant satisfaction and hence lead to possible repetitive works are identified and the results showed the existence of significant difference between clients and consultants perspectives regarding this issue as well. The framework presented within this paper aims to help the contracting organisations to compare and recognise the different approaches and perceptions of both clients and consultants during contractor qualification and selection processes. The contracting organisations in the related sectors will be able to use the framework provided within this study to recognise the overall demand in a more complete and better manner and hence formulate or modify strategies accordingly.

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