Comparative Experimental Study of Friction Parameters in a Tribopair and a Force System

The paper presents the results of experimental study of the effect of stresses resulting from off-contact load on variations in the friction torque and the coefficient of resistance to rolling in a force system compared to a similar tribopair. The results are compared with the theoretical data obtained on the basis of the deformation approach to the analysis of friction. It is shown that the calculation estimates agree well with the experimental results both qualitatively (the regularities) and quantitatively (the numerical values). The error of the determination of the coefficient of resistance to rolling does not exceed 7%. The study results make it possible to formulate and solve the problem of the effective control over the friction force (coefficient) by varying cyclic (bending) stresses

A Method of Experimental Study of Friction in a Active System

It is shown that machines of the SI series for wear-fatigue tests make it possible to measure the friction torque during rolling with a sufficient accuracy. For this purpose, methods for the calibration and determination of the accuracy of all parameters and characteristics being specified and measured are developed. A method for the determination of the coefficient of resistance to rolling depending on the value of the off-contact load is also developed and exemplified. Analysis of the experimental results and analytical description of the complex of these studies will be presented in subsequent papers

Clinical Symptoms in Fibromyalgia Are Better Associated to Lipid Peroxidation Levels in Blood Mononuclear Cells Rather than in Plasma

This is an open-access article distributed under the terms of the Creative Commons Attribution License.[Background] We examined lipid peroxidation (LPO) in blood mononuclear cells (BMCs) and plasma, as a marker of oxidative damage, and its association to clinical symptoms in Fibromyalgia (FM) patients. [Methods]: We conducted a case–control and correlational study comparing 65 patients and 45 healthy controls. Clinical parameters were evaluated using the Fibromyalgia Impact Questionnaire (FIQ), visual analogues scales (VAS), and the Beck Depression Inventory (BDI). Oxidative stress was determined by measuring LPO in BMCs and plasma. [Results]: We found increased LPO levels in BMCs and plasma from FM patients as compared to normal control (P<0.001). A significant correlation between LPO in BMCs and clinical parameters was observed (r = 0.584, P<0.001 for VAS; r = 0.823, P<0.001 for FIQ total score; and r = 0.875, P<0.01 for depression in the BDI). We also found a positive correlation between LPO in plasma and clinical symptoms (r = 0.452, P<0.001 for VAS; r = 0.578, P<0.001 for FIQ total score; and r = 0.579, P<0.001 for depression in the BDI). Partial correlation analysis controlling for age and BMI, and sex, showed that both LPO in cells and plasma were independently associated to clinical symptoms. However, LPO in cells, but not LPO in plasma, was independently associated to clinical symptoms when controlling for depression (BDI scores). [Discussion]: The results of this study suggest a role for oxidative stress in the pathophysiology of fibromyalgia and that LPO in BMCs rather than LPO in plasma is better associated to clinical symptoms in FM.This work was supported by Spanish FIS PI080500 grant, and FIS EC08/00076 grant, Ministerio de Sanidad, Spain, and Federación Andaluza de Fibromialgia y Fatiga Crónica (ALBA Andalucía). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe

Identification of Hydrodynamic Characteristics of the Spool-type Valve

Recently increased requirements for dynamic characteristics of hydraulic servo-drives demanded the use of nonlinear models, in addition to the linearized mathematical ones. Such models have to take into consideration the physical process features occurring in the hydraulic drive. However, references sometimes mention a discrepancy between the values of real natural frequency of oscillations and the theoretical value of natural oscillation frequency defined by the mathematical model, which takes into account only the standard nonlinearities. To identify reasons of abovementioned divergence the experiments have been conducted to study influence of flow unsteadiness on the auto-oscillation frequency of a hydraulic drive. Modern electrohydraulic throttle-controlled drives are usually equipped with the actuation (control) devices, which have operating speed much higher than that of the power part of a hydraulic drive. This circumstance allows us to use a mechanically controlled hydraulic drive to study the non-stationary characteristics of a spool-type valve. As a result of experiments, it has been found that the fluid flow unsteadiness can be taken into consideration through introducing the auto-oscillations of delay time into calculations.The pilot studied results have a scientific novelty because they for the first time define the influence of the fluid flow unsteadiness in the spool-type valve on dynamics of a hydraulic drive with throttle control.</p

Comparative Experimental Study of Friction Parameters in a Tribopair and a Force System

The paper presents the results of experimental study of the effect of stresses resulting from off-contact load on variations in the friction torque and the coefficient of resistance to rolling in a force system compared to a similar tribopair. The results are compared with the theoretical data obtained on the basis of the deformation approach to the analysis of friction. It is shown that the calculation estimates agree well with the experimental results both qualitatively (the regularities) and quantitatively (the numerical values). The error of the determination of the coefficient of resistance to rolling does not exceed 7%. The study results make it possible to formulate and solve the problem of the effective control over the friction force (coefficient) by varying cyclic (bending) stresses

A Method of Experimental Study of Friction in a Active System

It is shown that machines of the SI series for wear-fatigue tests make it possible to measure the friction torque during rolling with a sufficient accuracy. For this purpose, methods for the calibration and determination of the accuracy of all parameters and characteristics being specified and measured are developed. A method for the determination of the coefficient of resistance to rolling depending on the value of the off-contact load is also developed and exemplified. Analysis of the experimental results and analytical description of the complex of these studies will be presented in subsequent papers