Antalarmin

In the mol­ecule of the title compund [systematic name: N-butyl-N-ethyl-2,5,6-trimethyl-7-(2,4,6-trimethyl­phen­yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine], C24H34N4, the pyrrolopy­rimidine ring system is nearly planar, its five- and six-membered rings forming a dihedral angle of 5.3 (2)°. The benzene ring is nearly orthogonal to the central ring system. The N atom carrying the ethyl and n-butyl groups is flattened pyramidal

Superquadratic functions in several variables

AbstractThe concept of superquadratic functions in several variables, as a generalization of the same concept in one variable is introduced. Analogous results to results obtained for convex functions in one and several variables are presented. These include refinements of Jensen's inequality and its counterpart, and of Slater–Pečarić's inequality

Crossed helical gears with wheels from sintered steel with pyrohydrolysis

Crossed helical gears are used in cars and in many household appliances. The trend towards increased comfort in motor vehicles has led to the utilization of more than a hundred servo-drives in luxury class automobiles. Important advantages of the crossed helical gears are their easy and inexpensive design, good noise performance and high ratio that can be realized in one step. Sintered steel shows as very favorable material for wheels in crossed helical gears. High demands are set on gears made from sintered steel regarding wear, fretting, tooth fracture and pitting load capacity. This report shows results of iron-based sintered material Fe1.5Cr0.2Mo with pyrohydrolysis as additional treatment, in case of crossed helical gears concerning wear resistance and other damage types under different speed and load

Tribology Aspect of Rubber Shock Absorbers Development

Rubber is a very flexible material with many desirable properties Which enable its broad use in engineering practice. Rubber or rubber-metal springs are widely used as anti-vibration or anti-shock components in technical systems. Rubber-metal springs are usually realized as a bonded assembly, however especially in shock absorbers, it is possible to realize free contacts between rubber and metal parts. In previous research it authors was observed that friction between rubber and metal in such case have a significant influence on the damping characteristics of shock absorber. This paper analyzes the development process of rubber or rubber-metal shock absorbers realized free contacts between the constitutive parts, starting from the design, construction, testing and operation, with special emphasis on the development of rubber-metal springs for the buffing and draw gear of railway vehicles

Methods and Principles of Determining the Footwear and Floor Tribological Characteristics

There are many standards relating to the anti-slip properties of footwear and flooring. These standards describe the different test methods and procedures for determining the footwear and floor slip resistance in different conditions. In this paper authors systematize the standards in this field applied in the EU and in Serbia and cite the Serbian institutes which are certified for this type of testing. In addition, the authors have carried out an analysis and comparison of the tests that are defined in these standards, indicating their advantages and disadvantages. Importance of the static and kinetic friction testing in determining the anti-slip properties of footwear and flooring is specifically indicated. Considering the current standards in area of slip resistance of the footwear and floor covering authors have determined the testing conditions for laboratory measuring the friction forces of different floor and footwear materials. The laboratory measurement has carried out at Faculty of Mechanical Engineering in Niš. The measuring results and their analysis are presented in the paper, as well

Prediction of heat generation in transmission bearings by application of fem

Heat generation in bearings is manifested by the power losses of the transmission. Because of the rise in temperature due to heat generation, appearance of dilatation adversely affects the bearings geometrical characteristics. Heat generation has an adverse effect as well on the properties of lubricant, its efficiency of work and rheological characteristics. There are several ways for heat generation within rolling bearing: By friction between the rolling bodies and raceways, due to hydraulic resistance of lubricants, friction between the rolling bodies and cage, friction between the cage and rim of rings and friction between the seals and rings. This paper discusses the first of these five causes, which is considered to be dominant. By application of finite element method, the heat generation between the rolling bodies and raceways was predicted. Paper studies the influence of contact load and angular speed on the heat generation, while taking into the account the thermal properties of the bearing components. Based on performed numerical research a new method for prediction of heat generation in transmission bearings was proposed

Tribological Aspect of Rubber Based Parts used in Engineering

In most of the cases, the friction is considered as a negative side-effect concerning energy loss following every process of the power transmission. However, the friction has significant positive side effects, because it is an indispensable prerequisite for the movement of people, machines, transportation means and others. Efficiency of these movements mostly depends on the friction between rubber and different materials such as metals, concrete, earth, wood, plastic, etc. Certain standards relating to measurement and determination of the friction characteristics of rubber were established. However considering that tribology of the rubber is very complex problem, numerous studies around the world are conducted. This paper gives an overview of some of the existing standards and conducted researches in this area. The paper also provides an overview of theoretical and experimental studies of friction the rubber and the other materials, which are done at Faculty of Mechanical Engineering in Niš

Benign Epithelial Gastric Polyps – Frequency, Location, and Age and Sex Distribution

Prospective investigation has been undertaken with the aim to study the frequency, location and age and sex distribution of various histological types of benign gastric epithelial polyps. Histological type - adenomatous, hyperplastic and fundic gland polyps - was diagnosed on the basis of at least three histological samples taken from the polyp. Biopsy samples were also taken from the antrum and the body of the stomach so that gastritis could be graded and classified, and the presence of H. pylori could be determined by histology. All 6,700 patients, who had undergone upper gastrointestinal endoscopy in a one-year period, participated in this study. Among them 42 benign gastric epithelial polyp were found in 31 patients: adenomatous gastric polyps in 7 patients, hyperplastic gastric polyp in 21 and fundic gland polyp in 3 patients. All patients with hyperplastic polyps had chronic active superficial gastritis, whereas most of the patients with adenomatous polyps had a chronic atrophic gastritis with high prevalence of intestinal metaplasia. Among 21 patients with hyperplastic gastric polyps, 16 (76%) patients were positive for H. pylori infection in contrast to only 2 patients (29%) with adenomatous gastric polyps and 1 patient (33%) with fundic gland polyp. Presented data indicates that hyperplastic gastric polyps are the most common and they are associated with the presence of chronic active superficial gastritis and concomitant H. pylori infection. Adenomatous polyps are rarer and they tend to be associated with chronic atrophic gastritis and intestinal metaplasia. Fundic gland polyp is the rarest type of gastric polyps