The influence of surface treatment of PVD coating on its quality and wear resistant

The article deals with a determination of the influence of a cutting edge preparation on the quality and wear resistance of coated cutting tools. Cutting inserts made from a sintered carbide with a deposited layer of PVD coating were selected for measurement. Non-homogeneity caused by the creation of droplets arises in the application layer during the process of applying the coating by the PVD method. These droplets make the surface roughness of the PVD coating worse, increase the friction and thereby the thermal load of the cutting tool as well. Also, the droplets could be the cause of the creation and propagation of droplets in the coating and they can cause quick cutting tool wear during machining. Cutting edge preparations were suggested for the improvement of the surface integrity of deposited layers of PVD coating, namely the technology of drag finishing and abrasive jet machining. After their application, the areal surface roughness was measured on the surface of coated cutting inserts, the occurrence of droplets was tracked and the surface structure was explored. A tool-life test of cutting inserts was carried out for verification of the influence of surface treatment on the wear resistance of cutting inserts during the milling process. The cutting inserts with a layer of PVD coatings termed as samples A, B, and C were used for the tool-life test. The first sample, A, represented the coating before the application of cutting edge preparations and samples B and C were after the application of the cutting edge preparation. A carbon steel termed C45 was used for the milling process and cutting conditions were suggested. The visual control of surface of cutting inserts, intensity of wear and occurrence of thermal cracks in deposited PVD layers were the criterion for the evaluation of the individual tests.Web of Science97art. no. 43

Correlation between ultrasonic velocity and magnetic adaptive testing in flake graphite cast iron

A recently developed nondestructive method, called Magnetic Adaptive Testing was applied for investigation of flake graphite cast iron samples having various metallic matrices and graphite structures. MAT is typical by its low required magnetization of samples, because it is based on measurement of families of minor magnetic hysteresis loops. The flat samples were magnetized by an attached yoke and sensitive descriptors of their magnetic/structural state were obtained from evaluation of the measured data. Ultrasonic velocity measurements were performed and results of the non-destructive magnetic tests were compared with these data. A very good correlation was found between the magnetic descriptors and ultrasonic velocity.Web of Science667s17717

Nondestructive detection of local material thinning in ferromagnetic materials by Magnetic Adaptive Testing

A recently developed nondestructive method, called Magnetic Adaptive Testing, which is based on systematic measurement and evaluation of minor magnetic hysteresis loops was applied for detection of local material thinning in a thick, L-shaped ferromagnetic carbon steel, which simulates T-tubes with reinforcing plates. Artificially made slots were reliably detected with a good signal/noise ratio from the other side of the specimen, even through a covering ferromagnetic plate

Graviton propagators in AdS beyond GR: heat kernel approach

We present a new covariant method of construction of the (position space) graviton propagators in the $N$-dimensional (Euclidean) anti-de Sitter background for any gravitational theory with the Lagrangian that is an analytic expression in the metric, curvature, and covariant derivative. We show that the graviton propagators (in Landau gauge) for all such theories can be expressed using the heat kernels for scalars and symmetric transverse-traceless rank-2 tensors on the hyperbolic $N$-space. The latter heat kernels are constructed explicitly and shown to be directly related to the former if an improved bi-scalar representation is used. Our heat kernel approach is first tested on general relativity, where we find equivalent forms of the graviton propagators. Then it is used to obtain explicit expressions for graviton propagators for various higher-derivative as well as infinite-derivative/nonlocal theories of gravity. As a by-product, we also provide a new derivation of the equivalent action (correcting a mistake in the original derivation) and an extension of the quadratic action to arbitrary ${N\geq 3}$ dimensions.Comment: 35 page

Infinite derivative gravity resolves nonscalar curvature singularities

We explicitly demonstrate that the nonlocal ghost-free ultraviolet modification of general relativity (GR) known as the infinite derivative gravity (IDG) resolves nonscalar curvature singularities in exact solutions of the full theory. We analyze exact pp-wave solutions of GR and IDG describing gravitational waves generated by null radiation. Curvature of GR and IDG solutions with the same energy-momentum tensor is compared in parallel-propagated frames along timelike and null geodesics at finite values of the affine parameter. While the GR pp-wave solution contains a physically problematic nonscalar curvature singularity at the location of the source, the curvature of its IDG counterpart is finite.Comment: 5 pages, 1 figur

Heart rate response to game load of U19 female basketball players

The aim of the study is to compare the intensity of game load between player positions (guards, forwards, centers) and between the 1st and the 2nd half of the basketball games in female category U19. Ten female basketball players (17.6 ± 0.9 years old) participated in this study. The beep test was used to determine the maximal heart rate (HRmax) and based on the HRmax the four intensity zones were set ( 95% of HRmax). The heart rate (HR) and its development during the competition were monitored by telemetric device Suunto Team Pack. We did not record any statistical significance among player positions in particular intensity zones, nor in % of HRmax (86 ± 2.8 vs. 88.3 ± 2.9 vs. 87.7 ± 3.3; guards vs. forwards vs. centers). Moreover, when we compared the 1st and the 2nd half, of individual games, in particular zones and in % of HRmax (87.8 ± 3 vs. 86.8 ± 3.1) we also did not record any statistical significance. The female basketball players spent 74.3% of total time with HR greater than 85% of HRmax which indicates high physiological demands during the competition on all player positions. The results can be used for comparison with the intensity of training load and for optimizing the training process.This study was funded by the project Specific Research at Masaryk University (MUNI/A/0900/2013)

The role of spiral stabilization exercise on the level of postural stabilty

The main aim of our study was to find out if exercise of spiral stabilization can improve level of postural stability (PS). PS is often described as the ability to maintain center of gravity within the base of support and it is also a fundamental part in assessing the efficacy of intervention for improving balance. Both, static and dynamic PS is the result of relationship between proprioception, vision and vestibular system. These three main sources are responsible for position of the body during static or dynamic activity. The participants were randomly divided into an experimental group (11 girls; mean age=13.3±1.3 years; mean height=1.52±0.07 m; mean body weight=44.56±4.13 kg) and control group (11 girls; mean age=13.5±0.80 years; mean height=1.50±0.08 m; mean body weight=46.45±6.27 kg). At the beginning of the experiment, parents of participants signed the informed consent about participation on the programme. An electronic balance board was used for measuring PS. The exercise regimen was set up 4 times weekly for 3 months. The result of the study showed significant improvement in a level of postural stability in the experimental group (paired samples t-test; p=0.00989; the significance level 95%) and there is no significant improvement in the control group (p=0.25564; the significance level 95%).This paper was written at Masaryk university as part of the project "Monitoring of foot loading, body posture in relation to SM – System exercise for pupils of dance conservatoire" number MUNI/A/0854/2013 with the support of the Specific University Research Grant, as provided by the Ministry of Education, Youth and Sports of the Czech Republic in the year 2014

On paths and cycles dominating hypercubes

AbstractThe aim of the present paper is to study the properties of the hypercube related to the concept of domination. We derive upper and lower bounds and prove an interpolation theorem for related invariants