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The necessity of monitoring the abrasive waterjet (AWJ) processes increases with the spreading of this tool into the machining processes. The forces produced on the workpiece during the abrasive waterjet machining can yield some valuable information. Therefore, a special waterjet-force measuring device designed and produced in the past has been used for the presented research. It was tested during the AWJ cutting processes, because they are the most common and the best described up-to-date AWJ applications. Deep studies of both the cutting process and the respective force signals led to the decision that the most appropriate indication factor is the tangential-to-normal force ratio (TNR). Three theorems concerning the TNR were formulated and investigated. The first theorem states that the TNR strongly depends on the actual-to-limit traverse speed ratio. The second theorem claims that the TNR relates to the cutting-to-deformation wear ratio inside the kerf. The third theorem states that the TNR value changes when the cutting head and the respective jet axis are tilted so that a part of the jet velocity vector projects into the traverse speed direction. It is assumed that the cutting-to-deformation wear ratio increases in a certain range of tilting angles of the cutting head. This theorem is supported by measured data and can be utilized in practice for the development of a new method for the monitoring of the abrasive waterjet cutting operations. Comparing the tilted and the non-tilted jet, we detected the increase of the TNR average value from 1.28 ± 0.16 (determined for the declination angle 20° and the respective tilting angle 10°) up to 2.02 ± 0.25 (for the declination angle 30° and the respective tilting angle of 15°). This finding supports the previously predicted and published assumptions that the tilting of the cutting head enables an increase of the cutting wear mode inside the forming kerf, making the process more efficient.
- Klíčová slova
- abrasive waterjet, cutting wear, deformation wear, kerf characteristics, normal force, tangential force,
- Publikační typ
- časopisecké články MeSH
Cutting using an abrasive water jet is a complex process involving several physical phenomena. This research studies some of them, mostly the influence of selected variables on the measured forces and vibrations. The traverse speed represents one of the key parameters when cutting using the AWJ. In the presented research, a set of experiments was performed on twelve different metal samples, while the force sensor measured the exerted forces and accelerometers measured the vibrations. Ten different types of steel samples of the same dimensions were cut applying five different traverse speeds. The data obtained during these measurements show that an increase in the traverse speed leads to an increase in the measured forces and vibrations. An analogous experiment performed on bronze and duralumin samples of the same dimensions, having applied higher speeds to compensate for the difference in the material structure and properties, completes the presented data. The most important results of the research are that exerted forces in the z-axis are higher than those in the x-axis, whereas measured vibrations are higher in the x-axis. According to our research, the elemental structure, especially the carbide formation, affects the measured forces and vibrations substantially.
- Klíčová slova
- abrasive water jet, cutting, forces, normal force, tangential force, traverse speed, vibrations,
- Publikační typ
- časopisecké články MeSH
A detailed analysis of the in situ Raman spectroelectrochemical behavior of individual semiconducting single-walled carbon nanotubes (SWCNTs) is presented. Special attention has been paid to the development of the tangential (TG) mode frequency, which shifts when the externally applied potential Ve is shifted away from Ve=0. The magnitude and direction (upshift or downshift) of the tangential mode band has been found to be dependent on the diameter of the semiconducting tubes. For negative charging, the small-diameter tubes exhibit a downshift while the large-diameter tubes exhibit an upshift. This behavior is explained by a competition between two effects which cause opposite shifts in the TG mode frequency during negative charging: a phonon renormalization effect and a C-C bond weakening during the charging process. Positive charging always causes an upshift of the TG mode frequency. However, the magnitude of the upshift is dependent on the tube diameter.
- MeSH
- elektrochemie metody MeSH
- elektrody MeSH
- krystalizace MeSH
- mikroskopie elektronová rastrovací MeSH
- nanostruktury chemie MeSH
- nanotechnologie metody MeSH
- nanotrubičky uhlíkové chemie MeSH
- nanotrubičky chemie MeSH
- polovodiče * MeSH
- povrchové vlastnosti MeSH
- Ramanova spektroskopie MeSH
- testování materiálů MeSH
- uhlík chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- nanotrubičky uhlíkové MeSH
- uhlík MeSH
OBJECTIVE: Translation of the contact zone in articulating joints is an important component of joint kinematics, yet rarely investigated in a biological context. This study was designed to investigate how sliding contact areas affect cartilage mechanobiology. We hypothesized that higher sliding speeds would lead to increased extracellular matrix mechanical stress and the expression of catabolic genes. DESIGN: A cylindrical Teflon indenter was used to apply 50 or 100 N normal forces at 10, 40, or 70 mm/s sliding speed. Mechanical parameters were correlated with gene expressions using a multiple linear regression model. RESULTS: In both loading groups there was no significant effect of sliding speed on any of the mechanical parameters (strain, stress, modulus, tangential force). However, an increase in vertical force (from 50 to 100 N) led to a significant increase in extracellular matrix strain and stress. For 100 N, significant correlations between gene expression and mechanical parameters were found for TIMP-3 (r(2) = 0.89), ADAMTS-5 (r(2) = 0.73), and lubricin (r(2) = 0.73). CONCLUSIONS: The sliding speeds applied do not have an effect on the mechanical response of the cartilage, this could be explained by a partial attainment of the "elastic limit" at and above a sliding speed of 10 mm/s. Nevertheless, we still found a relationship between sliding speed and gene expression when the tissue was loaded with 100 N normal force. Thus despite the absence of speed-dependent mechanical changes (strain, stress, modulus, tangential force), the sliding speed had an influence on gene expression.
- Klíčová slova
- cells, chondrocytes, degradative enzymes, lubricin, mechanobiology, sliding contact,
- Publikační typ
- časopisecké články MeSH
The cause of décollement is usually considered to be tangential brute blunt force impacting the body surface especially in case of hitting or running-over injury of the pedestrian's body by a car. The term rolling effect or rolling mechanism is used as well. The dissociation of tissue layers with other epiphenomenon occurs. The presented group of 152 décollement determined in 103 autopsy cases during the 4 years period comprises the observation of décollement of different etiology of the injuries (traffic accidents, falls from the high, compression of the torso); in the traffic accidents the occurrence in various participants of the traffic, not only in the case of the collision of the pedestrians with various traffic vehicles, but also in drivers of various traffic vehicles, and fellow-travelers as well. The topic, the localization, the content, the extent, and vital reaction and combination injuries were followed-up. According to the variability of the injury etiology, not restricted to the traditional conception of the décollement mechanism, it is obvious that the passed on rule by far is not covering the whole content of this concept. We didn't find any alternative interpretation of until now presented mechanism in the literature. The medical literature focuses mostly on the clinical aspect of this injury. In this paper, the biomechanics of the décollement origin also in case of the tissue compression by the pressure applied perpendicularly to the body surface, the dependences on physical properties of the actively or passively affecting object, the relevance of the ratio of the tissue structures compression in one direction and transversal dilation in other two directions according to the Poisson's constant, the question of tangential factor of the force in case of vertical falling on the horizontal plane, and biomechanical relations in case of body landing on an oblique surface are discussed. The mechanism of décollement is more complex as presented until now. The forensic interpretation of findings should reflex the above-mentioned facts.
- MeSH
- biomechanika MeSH
- lidé MeSH
- soudní lékařství * MeSH
- tupá poranění etiologie patofyziologie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
Chaotic features of the macro-instability (MI) of flow patterns in stirred tanks are studied in this paper. Datasets obtained by measuring the axial component of the fluid velocity and the tangential force affecting the baffles are used. Two geometrically identical, flat-bottomed cylindrical mixing tanks (diameter of 0.3m) stirred with either pitched blade turbine impellers or Rushton turbine impeller are used in the experiments, and water and aqueous glycerol solutions are used as the working liquids. First, the presence of the MI component in the data is examined by spectral analysis. Then, the MI components are identified in the data using the proper orthogonal decomposition (POD) technique. The attractors of the macro-instability are reconstructed using either the POD eigenmodes or a method of delays and finally the attractor invariants are evaluated. The dependence of the correlation dimension and maximum Lyapunov exponent on the vessel operational conditions is determined together with their distribution within the tank. No significant spatial variability of the correlation dimension value is observed. Its value is strongly influenced by impeller speed and by the vessel-impeller geometry. More profound spatial distribution is displayed by the maximum Lyapunov exponent taking distinctly positive values. These two invariants, therefore, can be used to locate distinctive regions with qualitatively different MI dynamics within the stirred tank.
- Publikační typ
- časopisecké články MeSH
Atherosclerosis is associated with systemic risk factors such as arterial hypertension, hyperlipidemia, diabetes mellitus and smoking. Yet it is a focal disease, predominantly affecting predisposed areas. The principal local hemodynamic factor is wall shear stress, i.e. the frictional force acting tangentially on the endothelial cell surface. The effect of wall shear stress on the endothelium depends on its magnitude and direction, as well as on the local vessel geometry and blood flow characteristics. Wall shear stress is an important determinant of endothelial function and phenotype. The article deals with the influence of wall shear stress on endothelial cell function, atherosclerotic plaque formation, and vascular remodelling in the common carotid artery.
BACKGROUND: We evaluated visual outcomes after vitrectomy for diabetic cystoid macular edema and factors possibly influencing final visual acuity. MATERIALS AND METHODS: Studied prospectively, pars plana vitrectomy was performed on 72 consecutive eyes of 61 patients with diabetic cystoid macular edema not responsive to laser photocoagulation therapy. Vitreomacular traction was observed on biomicroscopy, B-scan ultrasonography, and optical coherence tomography in 21 eyes, 15 eyes had a complete posterior vitreous detachment (PVD) and 36 eyes had partial peripheral PVD. Vitrectomy with releasing vitreomacular tangential and axial tractional forces was performed. All patients were followed up for at least 6 months. RESULTS: The anatomical results were satisfactory in 69 of 72 eyes (96 %), the final visual acuity improved by 2 or more lines in 45 of 72 eyes (63 %), remained unchanged in 22 of 72 eyes (31 %), and deteriorated after surgery in 5 of 72 eyes (7 %), due to residual cystoid macular edema and massive macular hard exudates. The best results were obtained in edema with tractional predominance and in eyes with a duration of cystoid macular edema shorter than 6 months. CONCLUSIONS: Vitrectomy for diabetic cystoid macular edema is an effective procedure for reducing the edema and improving visual acuity. Surgery was beneficial not only in eyes with vitreomacular traction but also in eyes with complete PVD. Visual improvement after vitrectomy is related to duration of edema, therefore the timing of the surgery is an important prognostic factor.
- MeSH
- diabetická retinopatie diagnóza chirurgie MeSH
- lidé MeSH
- makulární edém diagnóza chirurgie MeSH
- následné studie MeSH
- odchlípení sítnice diagnóza chirurgie MeSH
- perforace sítnice diagnóza chirurgie MeSH
- pooperační komplikace etiologie MeSH
- vitrektomie * MeSH
- zraková ostrost MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
- práce podpořená grantem MeSH
