Contact Fatigue Analysis of a Dented Surface in a Dry Elastic–Plastic Circular Point Contact

The present article proposes a methodology for the computational analysis of damage induced in the vicinity of dents in a dry circular point contact under repeated rolling. The failure risk is evaluated through the use of the Dang Van multiaxial fatigue criterion. The dent is a typical surface defect encountered in rolling element bearings when operating in contaminated environments. It is usually created by a solid particle not removed by seals or filters when passing through an EHL conjunction. Since local plasticity occurs when the debris is first entrapped between the contacting surfaces, and later when the resulting dents are subjected to moving contact load, the elastic–plastic behavior of the material should be captured by the model. First, the dent shape and the subsurface stress and strain fields produced by the presence of a spherical particle are obtained by the finite element method. Second, the rolling of the load over the surface defect is simulated using a semi-analytical elastic–plastic code. The simulations are carried out for two different debris materials, both ductile but one significantly softer than the contacting surfaces, i.e., made of stainless steel 316L, the other one being made of bearing steel AISI 52100 similar to the contacting surfaces. The dent shape and initial stress and strain states are first presented. Subsequent stress and strain states after a few rolling cycles are then presented. Finally the effects of the coefficient of friction, presence of residual stress, and contact load magnitude are highlighted.     

Räumliche Charakterisierung der hydraulischen Leitfähigkeit in alluvialen Schotter-Grundwasserleitern: Ein Methodenvergleich

For groundwater transport modeling on a scale of 10–100 m, detailed information about the spatial distribution of hydraulic conductivity is of great importance. At a test site (10×20 m) in the alluvial gravel-and-sand aquifer of the perialpine Thur valley (Switzerland), four different methods were applied on different scales to assess this parameter. A comparison of the results showed that multilevel slug tests give reliable results at the required scale. For its analysis, a plausible value of the anisotropy ratio of hydraulic conductivity (K _v /K _h ) is needed, which was calculated using a pumping test. The integral results of pumping tests provide an upper boundary of the natural spectrum of hydraulic conductivity at the scale of the test site. Flowmeter logs are recommended if the relative distribution of hydraulic conductivity is of primary importance, while sieve analyses can be used if only a rough estimate of hydraulic conductivity is acceptable.     

Anwendung eines flexiblen Planungskonzepts für die Realisierung einer komplexen Baugrubensicherungsmaßnahme

A flexible planning concept for realization of a complex excavation safety measure. The excavation “Admonterhof” in the historical center of Graz is an example for technical and economical succcess of an exciting complicated structural design using a concept on the basis of the observational method. The intention to built a 20 m deep excavation beneath a protected monument was accompanied by some essential issues: the holding of the existing state without extensive movements by a girder grid of reinforced concrete, its support on large bored piles and small steel‐tube piles with possible active compensation of differential settlements, the general safety of the excavation in none built‐up areas with intersected bored piles, the underpinning of existing buildings with different structures by means of jet grouting, the exploration of the gradient and the permeability of a rock formation in a part of the excavation, retaining in the area of different solid tertiary with varying mechanical properties and the control of the inflow of ground water with more than 10m difference in level.     

Pathophysiological role of the cytokine network in the anterior pituitary gland

Recent evidence has demonstrated that cytokines and other growth factors act in the anterior pituitary gland. Using the traditional criteria employed to determine autocrine or paracrine functions our review shows that, in addition to their role as lymphocyte messengers, certain cytokines are autocrine or paracrine regulators of anterior pituitary function and growth. The cytokines known to regulate and/or be expressed in the anterior pituitary include the inflammatory cytokine family (IL-1 and its endogenous antagonist, IL-1ra; TNF-alpha, and IL-6), the Th1-cytokines (IL-2 and IFN-gamma), and other cytokines such as LIF, MIF, and TGF-beta. This review examines at the cellular, molecular, and physiological levels whether: (1) each cytokine alters some aspect of pituitary physiology; (2) receptors for the cytokine are expressed in the gland; and (3) the cytokine is produced in the anterior pituitary. Should physiological stimuli regulate pituitary cytokine production, this would constitute additional proof of their autocrine/paracrine role. In this context, we analyze in this review the current literature on the actions of cytokines known to regulate anterior pituitary hormone secretion, selecting the in vivo studies that support the direct action of the cytokine in the anterior pituitary. Further support for direct regulatory action is provided by in vitro studies, in explant cultures or pituitary cell lines. The cytokine receptors that have been demonstrated in the pituitary of several species are also discussed. The endogenous production of the homologous cytokines and the regulation of this expression are analyzed. The evidence indicating that cytokines also regulate the growth and proliferation of pituitary cells is reviewed. This action is particularly important since it suggests that intrinsically produced cytokines may play a role in the pathogenesis of pituitary adenomas. The complex cell to cell communication involved in the action of these factors is discussed.     

Robust Stability Analysis of Smith Predictor Based Interval Fractional-Order Control Systems: A Case Study in Level Control Process

The robust stability study of the classic Smith predictor-based control system for uncertain fractional-order plants with interval time delays and interval coefficients is the emphasis of this work.Interval uncertainties are a type of parametric uncertainties that cannot be avoided when modeling real-world plants.Also,in the considered Smith predictor control structure it is supposed that the controller is a fractional-order proportional integral derivative(FOPID) controller.To the best of the a...     

Mechanical properties of talc-filled polypropylene. Influence of filler content,filler particle size and quality of dispersion

Mechanical properties of polypropylene-talc composites are measured as a function of talc concentration up to 40 wt.-%, Young's modulus of filled polypropylene shows linear increase with talc concentration up to double the value of unfilled polymer. Yield stress and Charpy notch toughness decrease with increasing talc content below matrix level at the highest filler content. Composite ultimate tensile elongation and tensile impact strength decrease sharply beginning at the lowest filler concentration. The influence of the talc particle size on the mechanical properties, especially composite toughness, mentioned above, is investigated. Four type of talc were used. Notch toughness decreases according to a linear dependence with mean size of talc particles. Evaluating impact strength possible content of agglomerates of filler and other additions is necessary to be included: tensile impact strength gives slow linear dependence with increasing content of filler particles and/or agglomerates above about 10 μm. The influence of talc particle size on the toughness of filled polypropylene becomes strong if the rubber particles are present.     

Urinary Excretion of Ecdysterone and Its Metabolites Following Spinach Consumption

Scope

The phytosteroid ecdysterone is present in spinach. In this study, the urinary elimination of ecdysterone and its metabolites in humans is investigated following spinach consumption of two different culinary preparations.

Methods and results

Eight participants (four males, four females) ingested 950 (27.1) g sautéed spinach (average [±standard deviation (SD)]) and 912 (70.6) g spinach smoothie as second intervention after washout. Post-administration urines are analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). After intake of both preparations, ecdysterone and two metabolites, 14-deoxy-ecdysterone, and 14-deoxy-poststerone, are excreted in urine. The maximum concentration of ecdysterone is ranging from 0.09 to 0.41 µg mL⁻¹ after sautéed spinach and 0.08–0.74 µg mL⁻¹ after smoothie ingestion. The total excreted amount (mean% [±SD]) in the urine as a parent drug plus the metabolites is only 1.4 (1.0) for both sautéed spinach and smoothie. The apparent sex related differences in 14-deoxy-poststerone excretion will need further investigations.

Conclusion

Only a small proportion of ecdysterone from spinach is excreted into urine. No significant differences are found in concentration and recovered amount (%) of ecdysterone, 14-deoxy-ecdysterone, and 14-deoxy-poststerone in urine between sautéed spinach and smoothie ingestion. A discrimination between ecdysterone from food or preparations will be challenging based on urinary concentrations only, at least for later post-administration samples.     

Aerodynamic performance of a dual turbine concept characterized by a relatively close distance between rotors

In this work, a closely spaced dual turbine concept is studied. The distance between the two side-by-side hubs is 1.05 $D$, where $D$ is the rotor diameter. This configuration has a potential benefit for offshore wind developments in which power density can be maximized. The main goal is to evaluate the overall aerodynamic performance, blade loads, and wake structure of a reference wind turbine generator operating within this dual turbine configuration and to compare the effects against those for the typical single turbine configuration. For this purpose, an actuator line model has been employed together with the large eddy simulation approach for predicting the turbulence effects. This model was implemented by using the open-source computational fluid dynamics toolbox OpenFOAM. Results show a better performance for the dual turbine concept. Under same operating conditions, the aerodynamic power of each turbine within the dual concept is higher than the power of the stand alone turbine, particularly at lower operating wind speeds (approximately 2% to 3% of extra power per turbine). Comparison between the two configurations shows similar character of the tangential and normal forces acting on the blades in terms of magnitude and fluctuation, eliminating potential concerns regarding fatigue and blade design. The largest difference in the tangential and normal root bending moments are approximately 3% and 2%, respectively, between single and dual turbine configurations. Finally, wake recovery analysis shows a downwind velocity deficit that is not enhanced streamwise in the dual turbine configuration with no considerable difference after 7 $D$.     

Stabilizing region of fractional-order proportional integral derivative controllers for interval delayed fractional-order plants

This paper concentrates on computing the stabilizing region of fractional-order proportional integral derivative (FOPID) controllers for interval delayed fractional-order plants. An interval delayed fractional-order plant is defined as a fractional-order transfer function with a time delay whose denominator and numerator coefficients are all uncertain and lie in specified intervals. In the present study, first, a theorem is proven to analyze the robust stability of the given closed-loop. Then, a method is proposed to solve the problem of robustly stabilizing interval delayed fractional-order plants by using FOPID controllers. Moreover, two auxiliary functions are presented to fulfill the additional specifications of design, ensuring better performance of the controlled system with respect to the disturbance and noise. Finally, two examples are provided to illustrate the design procedure.     

Triangle Influence Supersets for Fast Distance Computation

We present an acceleration structure to efficiently query the Signed Distance Field (SDF) of volumes represented by triangle meshes. The method is based on a discretization of space. In each node, we store the triangles defining the SDF behaviour in that region. Consequently, we reduce the cost of the nearest triangle search, prioritizing query performance, while avoiding approximations of the field. We propose a method to conservatively compute the set of triangles influencing each node. Given a node, each triangle defines a region of space such that all points inside it are closer to a point in the node than the triangle is. This property is used to build the SDF acceleration structure. We do not need to explicitly compute these regions, which is crucial to the performance of our approach. We prove the correctness of the proposed method and compare it to similar approaches, confirming that our method produces faster query times than other exact methods.