Homogenization of the Equations Governing the Flow Between a Slider and a Rough Spinning Disk

We have analyzed the behavior of the flow between a slider bearing and a hard-drive magnetic disk under two types of surface roughness. For both cases the length scale of the roughness along the surface is small as compared to the scale of the slider, so that a homogenization of the governing equations was performed. For the case of longitudinal roughness, we derived a one-dimensional lubrication-type equation for the leading behavior of the pressure in the direction parallel to the velocity of the disk. The coefficients of the equation are determined by solving linear elliptic equations on a domain bounded by the gap height in the vertical direction and the period of the roughness in the span-wise direction. For the case of transverse roughness the unsteady lubrication equations were reduced, following a multiple scale homogenization analysis, to a steady equation for the leading behavior of the pressure in the gap. The reduced equation involves certain averages of the gap height, but retains the same form of the usual steady, compressible lubrication equations. Numerical calculations were performed for both cases, and the solution for the case of transverse roughness was shown be in excellent agreement with a corresponding numerical calculation of the original unsteady equations

A Dynamic Energy Budget Model of Ornate Box Turtle Shell Growth

Many aspects of box turtle development may depend on size rather than age. Notable examples include sexual maturity and the development of the fully closing hinge in the shell that allows box turtles to completely hide in their shells. Thus, it is important to understand how turtles grow in order to have a complete understanding of turtle biology. Previous studies show that turtle shell growth behaves in a logistic manner. These studies use functional models that fit the data well but do little to explain mechanisms. In this work we use the ideas found in dynamic energy budget theory to build a model of box turtle shell growth. We show this model fits the data as well as previous models for ornate box turtles Terrapene ornata ornata, but also offers explanations for observed phenomena, such as maximum sizes and the appearance of biphasic growth

Kosowo, mit kosowski i jego recepcja

Artykuł traktuje o tak zwanym micie kosowskim, który został stworzony na kanwie czternastowiecznej bitwy na Kosowym Polu. Mówi o tworzeniu się tego mitu, o poszczególnych osobach stojących za nim oraz o wpływie wydarzeń historycznych, które miały wpływ na redagowanie go, a przede wszystkim o roli Kosowa w budowaniu świadomości narodowej Serbów, jego roli, oraz o jego recepcji we współczesnym społeczeństwie serbskim. Nie ogranicza się jedynie do wydarzeń historyczno‑politycznych, ale stara się w sposób możliwie najszerszy przybliżyć czytelnikowi problem mitu

Systems biology of platelet-vessel wall interactions

Platelets are small, anucleated cells that participate in primary hemostasis by forming a hemostatic plug at the site of a blood vessel's breach, preventing blood loss. However, hemostatic events can lead to excessive thrombosis, resulting in life-threatening strokes, emboli, or infarction. Development of multi-scale models coupling processes at several scales and running predictive model simulations on powerful computer clusters can help interdisciplinary groups of researchers to suggest and test new patient-specific treatment strategies

Terrestrial capture of prey by the reedfish, a model species for stem tetrapods

Due to morphological resemblance, polypterid fishes are used as extant analogues of Late Devonian lobe‐finned sarcopterygians to identify the features that allowed the evolution of a terrestrial lifestyle in early tetrapods. Previous studies using polypterids showed how terrestrial locomotion capacity can develop, and how air ventilation for breathing was possible in extinct tetrapodomorphs. Interestingly, one polypterid species, the reedfish Erpetoichthys calabaricus, has been noted being capable of capturing prey on land. We now identified the mechanism of terrestrial prey‐capture in reedfish. We showed that this species uses a lifted trunk and downward inclined head to capture ground‐based prey, remarkably similar to the mechanism described earlier for eel‐catfish. Reedfish similarly use the ground support and flexibility of their elongated body to realize the trunk elevation and dorsoventral flexion of the anterior trunk region, without a role for the pectoral fins. However, curving of the body to lift the trunk may not have been an option for the Devonian tetrapodomorphs as they are significantly less elongated than reedfish and eel‐catfish. This would imply that, in contrast to the eel‐like extant species, evolution of the capacity to capture prey on land in early tetrapods may be linked to the evolution of the pectoral system to lift the anterior part of the body

Elevated hematocrit enhances platelet accumulation following vascular injury

Red blood cells (RBCs) demonstrate procoagulant properties in vitro, and elevated hematocrit is associated with reduced bleeding and increased thrombosis risk in humans. These observations suggest RBCs contribute to thrombus formation. However, effects of RBCs on thrombosis are difficult to assess because humans and mice with elevated hematocrit typically have coexisting pathologies. Using an experimental model of elevated hematocrit in healthy mice, we measured effects of hematocrit in 2 in vivo clot formation models. We also assessed thrombin generation, platelet-thrombus interactions, and platelet accumulation in thrombi ex vivo, in vitro, and in silico. Compared with controls, mice with elevated hematocrit (RBCHIGH) formed thrombi at a faster rate and had a shortened vessel occlusion time. Thrombi in control and RBCHIGH mice did not differ in size or fibrin content, and there was no difference in levels of circulating thrombin-antithrombin complexes. In vitro, increasing the hematocrit increased thrombin generation in the absence of platelets; however, this effect was reduced in the presence of platelets. In silico, direct numerical simulations of whole blood predicted elevated hematocrit increases the frequency and duration of interactions between platelets and a thrombus.Whenhumanwhole blood was perfused over collagen at arterial shear rates, elevating the hematocrit increased the rate of platelet deposition and thrombus growth. These data suggest RBCs promote arterial thrombosis by enhancing platelet accumulation at the site of vessel injury. Maintaining a normal hematocrit may reduce arterial thrombosis risk in humans

Expert recommendations on the assessment of wall shear stress in human coronary arteries : existing methodologies, technical considerations, and clinical applications

The aim of this manuscript is to provide guidelines for appropriate use of CFD to obtain reproducible and reliable wall shear stress maps in native and instrumented human coronary arteries. The outcome of CFD heavily depends on the quality of the input data, which include vessel geometrical data, proper boundary conditions, and material models. Available methodologies to reconstruct coronary artery anatomy are discussed in ‘Imaging coronary arteries: a brief review’ section. Computational procedures implemented to simulate blood flow in native coronary arteries are presented in ‘Wall shear stress in native arteries’ section. The effect of including different geometrical scales due to the presence of stent struts in instrumented arteries is highlighted in ‘Wall shear stress in stents’ section. The clinical implications are discussed in ‘Clinical applications’ section, and concluding remarks are presented in ‘Concluding remarks’ section

Analysis of a Hydrophobic Coating as Passive Anti-ice Solution for Wind Turbines

The future of energy production lies in renewable energy sources, and one of them is wind power. However, cold climates around the world are quite challenging when it comes to harnessing the wind for power production. The icing of turbine blades and anemometers often bring turbines to a grinding halt, which of course leads to significant production losses. Possible solutions for this problem include active and passive approaches. In this thesis, a new hydrophobic coating that could work as a passive anti-ice solution for wind turbine applications was analyzed. Actual anti-ice properties could not be investigated due to lack of requisite equipment, but a number of mechanical properties also important for assessing the functionality of the coating were studied. In addition, surface drying times at a constant temperature and different levels of humidity were determined to learn more about the curing behavior of the coating. Testing was carried out both on-site on a 1 MW turbine situated in Kotka, Finland as well as under laboratory conditions. The on-site testing involved the coating of test areas on turbine blades and subsequent inspections, and the laboratory testing followed procedures described in international standards as closely as possible. The results showed a very good performance of the coating in terms of material properties such as adhesion, film hardness and dirt repelling tested in this study. This contributes to the completion of the material database and encourages to the execution of further testing to create a version of the coating that is fully employable on wind turbines.Uusiutuvat energianlähteet ovat energiantuotannon tulevaisuus, ja tuulivoima kuuluu samaan joukkoon. Kylmät ilmastot ympäri maailmaa kuitenkin asettavat omat haasteensa tuulivoiman hyödyntämiselle. Siipien ja anemometrien jäätyminen aiheuttaa usein merkittäviä tuotannon menetyksiä, sillä se voi johtaa tuulivoimalan pysähtymiseen. Ongelman mahdollisiin ratkaisumalleihin kuuluu sekä aktiivisia että passiivisia lähestymistapoja. Opinnäytetyössä analysoitiin uudenlaista hydrofobista pinnoitetta, joka voisi toimia passiivisena jäätymisenestoratkaisuna tuulivoimasovelluksissa. Tarvittavien laitteiden puuttumisen takia varsinaisia jäätymisenesto-ominaisuuksia ei voitu tutkia, mutta muutamia pinnoitteen toimivuuden arvioimiselle tärkeitä mekaanisia ominaisuuksia tarkastettiin. Lisäksi määritettiin pintakuivumisaikoja vakiolämpötilalla ja eri ilmankosteusprosenteilla, jotta voitaisiin saada lisätietoja pinnoitteen kuivumiskäyttäytymisestä. Testaus tapahtui sekä 1 MW:n tuulivoimalalla Kotkassa että laboratorio-olosuhteissa. Kenttäkokeessa pinnoitettiin koealueita voimalan siivistä, ja niitä käytiin myöhemmin tarkastamassa kaksi kertaa. Laboratoriokokeet seurasivat mahdollisimman tarkasti kansainvälisissä standardeissa kuvattuja menettelyjä. Tulokset osoittivat pinnoitteen toimivan erittäin hyvin materiaaliominaisuuksien, kuten adheesion, kalvokovuuden ja lianhylkivyyden, suhteen. Tämä edistää materiaalitietopankin täydentämistä ja kannustaa suorittamaan lisää testejä pinnoitteen kaupallisen version kehittämiseksi tuulivoimasovelluksiin sopivaksi