Contact detection approach between wheel and rail surfaces

This work presents a general formulation to identify the contact points for the interaction between wheels and rails in the context of railway dynamics simulations. This formulation treats the wheel and rail as parametric surfaces and searches the contact between each wheel strip and the rail independently to avoid the numerical difficulties due to the wheel concave zone. This methodology assumes the rail as locally straight and takes advantage that its potential contacting surface is always convex. For the evaluation of contact forces, two Hertzian-based models are employed for normal and creep forces. A trailer vehicle running on a curved track is used to demonstrate the effectiveness of this methodology.The first authorissupported by the Portuguese Foundation for Science and Technology (FCT) under grant PD/BD/114154/2016.This work is also supported by FCT with the reference project UIDB/04436/202

Detection of Keratoconus With a New Biomechanical Index

To evaluate the ability of a new combined biomechanical index called the Corvis Biomechanical Index (CBI) based on corneal thickness profile and deformation parameters to separate normal from keratoconic patients

Choroidal and retinal structural, cellular and vascular changes in a rat model of Type 2 diabetes

Increasing evidence points to inflammation as a key factor in the pathogenesis of diabetic retinopathy (DR). Choroidal changes in diabetes have been reported and several attempts were made to validate in vivo choroidal thickness (CT) as a marker of retinopathy. We aimed to study choroidal and retinal changes associated with retinopathy in an animal model of spontaneous Type 2 diabetes, Goto-Kakizaki (GK) rats. Sclerochoroidal whole mounts and cryosections were prepared from 52-week-old GK and age-matched control Wistar Han rats. CT was measured by optical coherence tomography. Microglia reactivity, pericyte and endothelial cells distribution, and immunoreactivity of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2) were evaluated by immunofluorescence. Choroidal vessels were visualized by direct perfusion with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). Choroidal vascular density was evaluated by fluorescence microscopy. GK rats had increased CT (58.40 ± 1.15 μm versus 50.90 ± 1.58 μm, p < 0.001), reduced vascular density of the choriocapillaris (CC) (p = 0.045), increased Iba1+ cells density in the outer retina (p = 0.003) and increased VEGFR2 immunoreactivity in most retinal layers (p = 0.021 to 0.037). Choroidal microglial cells and pericytes showed polarity in their distribution, sparing the innermost choroid. This cell-free gap in the inner choroid was more pronounced in GK rats. In summary, GK rats have increased CT with decreased vascular density in the innermost choroid, increased VEGFR2 immunoreactivity in the retina and increased Iba1+ cells density in the outer retina.info:eu-repo/semantics/publishedVersio

Modelling Deformations in Car Crash animation

In this paper, we present a prototype of a deformation engine to efficiently model and render the damaged structure of vehicles in crash scenarios. We introduce a novel system architecture to accelerate the computation, which is traditionally an extremely expensive task. We alter a rigid body simulator to predict trajectories of cars during a collision and formulate a correction procedure to estimate the deformations of the collapsed car structures within the contact area. Non-linear deformations are solved based on the principle of energy conservation. Large plastic deformations resulting from collisions are modelled as a weighted combination of deformation examples of beams which can be produced using classical mechanics

Influence of the contact–impact force model on the dynamic response of multi-body systems

This work deals with contact–impact force models for both spherical and cylindrical contact surfaces. The incorporation of the friction phenomenon, based on the Coulomb friction law, is also discussed together with an effective computational strategy, which includes the automatic step size selection procedure. Impacts within a revolute clearance joint in a basic slider–crank mechanism are used as an example to compare the different contact force models. The collision is a prominent phenomenon in manymulti-body systems such as mechanisms with intermittent motion, kinematic discontinuities, and clearance joints. As a result of an impact, the values of the system state variables change very fast, eventually looking like discontinuities in the system velocities and accelerations. The impact is characterized by large forces that are applied and removed in a short time period. The knowledge of the peak forces developed in the impact process is very important for the dynamic analysis of multibody systems and it has consequences in the design process. The model for the contact–impact force must consider the material and geometric properties of the colliding surfaces, consider information on the impact velocity, contribute to an efficient integration, and account for some level of energy dissipation. These characteristics are ensured with a continuous contact force model, in which the deformation and contact forces are considered as continuous functions.FEDER - Project POCTI/2001/EME/38281.Fundação para a Ciência e a Tecnologia (FCT)

Elevated glucose changes the expression of ionotropic glutamate receptor subunits and impairs calcium homeostasis in retinal neural cells

PURPOSE. Altered glutamatergic neurotransmission and calcium homeostasis may contribute to retinal neural cell dysfunction and apoptosis in diabetic retinopathy (DR). The purpose of this study was to determine the effect of high glucose on the protein content of -amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate glutamate receptor subunits, particularly the GluR2 subunit, because it controls Ca2 permeability of AMPA receptor-associated channels. The effect of high glucose on the concentration of cytosolic free calcium ([Ca2 ]i) was also investigated. METHODS. The protein content of GluR1, GluR2, GluR6/7, and KA2 subunits was assessed by Western blot. Cobalt staining was used to identify cells containing calcium/cobalt-permeable AMPA receptors. The [Ca2 ]i changes evoked by KCl or kainate were recorded by live-cell confocal microscopy in R28 cells and in primary cultures of rat retina, loaded with fluo-4. RESULTS. In primary cultures, high glucose significantly decreased the protein content of GluR1 and GluR6/7 subunits and increased the protein content of GluR2 and KA2 subunits. High glucose decreased the number of cobalt-positive cells, suggesting a decrease in calcium permeability through AMPA receptor-associated channels. In high-glucose–treated cells, changes in [Ca2 ]i were greater than in control cells, and the recovery to basal levels was delayed. However, in the absence of Na , to prevent the activation of voltage-sensitive calcium channels, the [Ca2 ]i changes evoked by kainate in the presence of cyclothiazide, which inhibits AMPA receptor desensitization, were significantly lower in high-glucose–treated cells than in control cultures, further indicating that AMPA receptors were less permeable to calcium. Mannitol, used as an osmotic control, did not cause significant changes compared with the control. CONCLUSIONS. The results suggest that elevated glucose may alter glutamate neurotransmission and calcium homeostasis in the retina, which may have implications for the mechanisms of vision loss in DR.Foundation for Science and Technology, Portugal and FEDER (Grant POCTI/CBO/38545/01), The Juvenile Diabetes Research Foundation, The American Diabetes Association and the Pennsylvania Lions Sight Conservation and Eye Eye Research Foundation

Corneal Biomechanics in Ectatic Diseases: Refractive Surgery Implications.

BACKGROUND: Ectasia development occurs due to a chronic corneal biomechanical decompensation or weakness, resulting in stromal thinning and corneal protrusion. This leads to corneal steepening, increase in astigmatism, and irregularity. In corneal refractive surgery, the detection of mild forms of ectasia pre-operatively is essential to avoid post-operative progressive ectasia, which also depends on the impact of the procedure on the cornea. METHOD: The advent of 3D tomography is proven as a significant advancement to further characterize corneal shape beyond front surface topography, which is still relevant. While screening tests for ectasia had been limited to corneal shape (geometry) assessment, clinical biomechanical assessment has been possible since the introduction of the Ocular Response Analyzer (Reichert Ophthalmic Instruments, Buffalo, USA) in 2005 and the Corvis ST (Oculus Optikgerate GmbH, Wetzlar, Germany) in 2010. Direct clinical biomechanical evaluation is recognized as paramount, especially in detection of mild ectatic cases and characterization of the susceptibility for ectasia progression for any cornea. CONCLUSIONS: The purpose of this review is to describe the current state of clinical evaluation of corneal biomechanics, focusing on the most recent advances of commercially available instruments and also on future developments, such as Brillouin microscopy.(undefined)info:eu-repo/semantics/publishedVersio

Ghost dynamics in the soft gluon limit

We present a detailed study of the dynamics associated with the ghost sector of quenched QCD in the Landau gauge, where the relevant dynamical equations are supplemented with key inputs originating from large-volume lattice simulations. In particular, we solve the coupled system of Schwinger-Dyson equations that governs the evolution of the ghost dressing function and the ghost-gluon vertex, using as input for the gluon propagator lattice data that have been cured from volume and discretization artifacts. In addition, we explore the soft gluon limit of the same system, employing recent lattice data for the three-gluon vertex that enters in one of the diagrams defining the Schwinger-Dyson equation of the ghost-gluon vertex. The results obtained from the numerical treatment of these equations are in excellent agreement with lattice data for the ghost dressing function, once the latter have undergone the appropriate scale-setting and artifact elimination refinements. Moreover, the coincidence observed between the ghost-gluon vertex in general kinematics and in the soft gluon limit reveals an outstanding consistency of physical concepts and computational schemes.Comment: 34 pages, 12 figure

Loss of the Y chromosome in male patients with Myeloid Neoplasms

Loss of the Y chromosome (L0Y) is describe as a both a normal age – related event and a marker of a neoplastic clone in haematological diseases. In order to understand the relationship between L0Y chromosome and the different myeloid neoplasms, we retrospectively analysed cytogenetic results of 891 males’ patients, from 1995 to 2016 with myeloid neoplasms. Sixty one patients showed L0Y. Of the 61 patients without Y chromosome 24 (2,7%) had Myelodysplastic Syndromes (MDS); 24 (2,7%) had Myeloproliferative Neoplasms (MN); 6 (0,67%) had Neoplasm Myelodysplastic Syndrome / Myeloproliferative Neoplasms (MDS/MN) and 7 (0,79%) had Acute Myeloid Leukaemia (AML). These percentages can be different if we consider only the pathology in which was found the L0Y: 7,7% of all patients with MDS (310); 6,1% of all patients with NM (391); 6,6% in the patients with MDS/MN (90) and 7,6% in patients with AML (92). There are few reports of L0Y associated with Myeloid Neoplasms, since this has been considered mainly an age-related event. There for the tendency of L0Y in our data, seems to indicate that careful consideration should be taken when evaluating male patients with L0Y.N/