Film Thickness Modulations in Starved Elastohydrodynamically Lubricated Contacts Induced by Timne-Varying Lubricant Supply

Many elastohydrodynamically lubricated contacts in practical applications, e.g., in bearings, operate in the starved lubrication regime. As a result their performance is sensitive to variations of the lubricant layers present on the surfaces, which form the supply to the contact. Their shape is often determined by previous overrollings of the track and also by replenishment mechanisms and various migration effects. Variations of the layers induced in the direction of rolling lead to a time-varying lubricant supply to the contact. In this paper, by means of numerical simulations using a starved lubrication model, the film thickness modulations in the center of the contact induced by a harmonically varying inlet supply have been investigated. First, for a given load condition and layer wavelength, the effect of the nominal layer thickness (degree of starvation) and the layer variation amplitude is illustrated. Subsequently, using results for different load conditions, wavelengths, and degrees of starvation, it is shown that the response of the contact to such variations is determined by a nondimensional parameter, which represents the ratio of the entrainment length of the contact to the wavelength of the induced variation, and by the degree of starvation. A simple formula is presented for use in engineering predicting the ratio of the amplitude of the film modulations in the center of the contact to the amplitude of the layer variations in the inlet

MRI-based biomechanical parameters for carotid artery plaque vulnerability assessment.

Carotid atherosclerotic plaques are a major cause of ischaemic stroke. The biomechanical environment to which the arterial wall and plaque is subjected to plays an important role in the initiation, progression and rupture of carotid plaques. MRI is frequently used to characterize the morphology of a carotid plaque, but new developments in MRI enable more functional assessment of carotid plaques. In this review, MRI based biomechanical parameters are evaluated on their current status, clinical applicability, and future developments. Blood flow related biomechanical parameters, including endothelial wall shear stress and oscillatory shear index, have been shown to be related to plaque formation. Deriving these parameters directly from MRI flow measurements is feasible and has great potential for future carotid plaque development prediction. Blood pressure induced stresses in a plaque may exceed the tissue strength, potentially leading to plaque rupture. Multi-contrast MRI based stress calculations in combination with tissue strength assessment based on MRI inflammation imaging may provide a plaque stress-strength balance that can be used to assess the plaque rupture risk potential. Direct plaque strain analysis based on dynamic MRI is already able to identify local plaque displacement during the cardiac cycle. However, clinical evidence linking MRI strain to plaque vulnerability is still lacking. MRI based biomechanical parameters may lead to improved assessment of carotid plaque development and rupture risk. However, better MRI systems and faster sequences are required to improve the spatial and temporal resolution, as well as increase the image contrast and signal-to-noise ratio.This is the author accepted manuscript. The final version is available from Schattauer via http://dx.doi.org/10.1160/TH15-09-071

Clinical competence in performing and recognising a mediolateral episiotomy of protective angle and length: a systematic review

Objective: It is assumed that all doctors and midwives understand and apply evidence‐based principles in performing episiotomies in their everyday practice. However, remarkable discrepancies between even the most reputable literature sources in defining and describing the technique of performing mediolateral episiotomy (MLE) suggest that there is much ambiguity and confusion for both researchers and clinicians alike. Design: The systematic review protocol was written prior to starting the review and registered in the international prospective register of systematic reviews (PROSPERO/ID CRD42017070523) last updated on December 15, 2017. The review is reported using the Preferred Reporting Items for Systematic Reviews and Meta‐Analysis (PRISMA) guidelines. Methods: A database search was performed using: Medline, CINAHL, Scopus, Informit, the Cochrane Library and PubMed from database inception to 17 September 2017, with a final search on 10 February 2017. Studies were included if they examined clinicians' competency in performing an 'ideal' or 'correct' mediolateral episiotomy, as well as those studies that compared the performance of different professional roles. Studies usually defined an 'ideal' incision as one that met the criteria of an acceptable angle of incision from the midline, starting incision point distance from the midline and in terms of the length of the incision created. Results: While many of the studies included in this review were not of high quality (author self‐assessment) and had their own study criteria for a MLE, the literature suggests clinicians are generally unable to perform or simulate episiotomies within such standards. Overall, most of the literature reported doctors were performing more 'ideal', lateral and longer incisions compared to midwives; however, there were studies that found the opposite, showing statistically significant results in favour of midwives performing more protective episiotomies. There was no association between clinicians' participation in formal training courses and their ability to perform the 'ideal' incision, though one study did find an increased number of episiotomies performed under supervision improved clinicians competency. Conclusion: The obvious lack of understanding around defining and performing MLE for clinicians of various professional roles suggests the need to produce a uniform set of guidelines, and to develop a universal, low‐cost approach for teaching and performing the MLE technique in any clinical environment around the world

Stabilized vortex solitons in layered Kerr media

In this letter we demonstrate the possibility of stabilizing beams with angular momentum propagating in Kerr media. Large propagation distances without filamentation can be achieved in layered media with alternating focusing and defocusing nonlinearities. Stronger stabilization can be obtained with the addition of an incoherent beam.Comment: 4 pages, 3 figures. We have removed the sentence "Thus, they erroneously point out to the existence of fully stabilized vortex solitons" in page 2, column 2, line 7-8, because it might be confusin

Minor influence of humeral component size on torsional stiffness of the Souter-Strathclyde total elbow prosthesis

The use of Souter-Strathclyde total elbow prostheses is a well-studied replacement therapy for reconstruction of the elbow, but loosening of the humeral component is still of concern at long-term follow-up. In this study we looked at the effect of humeral component size and bone mineral density with respect to the bone size, torsional stiffness and torque to failure in cadaveric bones. Fourteen cadaveric humeri were available for testing purposes and four different humeral component size categories were used. First, we calculated the bone quality using dual-energy X-ray absorptiometry (DEXA). The torsional stiffness of the prosthetic humeri was measured during two mechanical tests: Firstly, the applied torque was recorded during a torsion fatigue test. The change of torsional stiffness between the tenth and last cycle was calculated. Secondly, a simple torsion test was performed and the torque to failure was recorded. No significant differences in outcome were seen between sizes of humeral components, even after correction for the bone size. Torsional stiffness and torque to failure were significantly correlated with bone mineral density and not with component size. In conclusion, bone quality seems to be a major eminent factor in the fixation of the humeral component in elbow replacement surgery

Effect of balloon angioplasty in femoropopliteal arteries assessed by intravascular ultrasound

Objective:To study the effects of balloon angioplasty (PTA) of the femoropopliteal artery with intravascular ultrasound (IVUS).Materials and methods:Corresponding IVUS cross-sections (n = 1033) obtained before and after PTA from 115 procedures were analysed. Vascular damage including plaque rupture, dissection and media rupture was assessed. Free lumen area (FLA), media-bounded area (MBA) and plaque area (PLA) were measured.Results:After PTA vascular damage was seen at the target site in 83 (72%) arteries: plaque rupture in 30 (26%), dissection in 66 (57%) and media rupture in 20 (17%) arteries. The FLA increased from 5.4 ± 3.4 mm2 to 14.1 ± 5.0 mm2 (p<0.001), MBA increased from 26.9 ± 10.0 mm2 to 32.9 ± 10.7 mm2 (p<0.001) and PLA decreased from 21.6 ± 8.5 mm2 to 18.8 ± 8.0 mm2 (p<0.001). The increase in MBA accounted for 68% of lumen gain. The frequency of vascular damage and the relative contribution of MBA increase and PLA decrease to luminal gain were not different in procedures with balloon diameter ≤ 5 mm and ≥ 6 mm.Conclusions:Vascular damage is common following PTA. Lumen gain is mainly due to vessel expansion and, to a lesser extent, to a decrease in plaque area

Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates

A quantized vortex dipole is the simplest vortex molecule, comprising two counter-circulating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasi-periodic behavior, in which the vortex lines undergo stable epicyclic orbits.Comment: 4 pages, 2 figure