Flow-induced elastic anisotropy of metallic glasses

As-cast bulk metallic glasses are isotropic, but anisotropy can be induced by thermomechanical treatments. For example, the diffraction halo in the structure function S(Q) observed in transmission becomes elliptical (rather than circular) after creep in uniaxial tension or compression. Published studies associate this with frozen-in anelastic strain and bond-orientational anisotropy. Results so far are inconsistent on whether viscoplastic flow of metallic glasses can induce anisotropy. Preliminary diffraction data suggest that the anisotropy, if any, is very low, while measurements of the elastic properties suggest that there is induced anisotropy, opposite in sign to that due to anelastic strain. We study three bulk metallic glasses, Ce65Al10Cu20Co5, La55Ni10Al35, and Pd40Ni30Cu10P20. By using resonant ultrasound spectroscopy to determine the full elasticity tensor, the effects of relaxation and rejuvenation can be reliably separated from uniaxial anisotropy (of either sign). The effects of viscoplastic flow in tension are reported for the first time. We find that viscoplastic flow of bulk metallic glasses, particularly in tension, can induce significant anisotropy that is distinct from that associated with frozen-in anelastic strain. The conditions for inducing such anisotropy are explored in terms of the Weissenberg number (ratio of relaxation times for primary relaxation and for shear strain rate). There is a clear need for further work to characterize the structural origins of flow-induced anisotropy and to explore the prospects for improved mechanical and other properties through induced anisotropy.This research was supported by the Engineering and the Engineering and Physical Sciences Research Council, UK (grant EP/I035404/1). Y.H.S. acknowledges support from a China Scholarship Council (CSC) scholarship. The authors thank Z. Lu, H. Y. Bai and W. H. Wang for the supply of the Ce65Al10Cu20Co5 and La55Ni20Al25 metallic glasses.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.actamat.2016.04.02

Simultaneous determination of wave speed and arrival time of reflected waves using the pressure-velocity loop

This is the post print version of the article. The official published version can be found at the link below.In a previous paper we demonstrated that the linear portion of the pressure–velocity loop (PU-loop) corresponding to early systole could be used to calculate the local wave speed. In this paper we extend this work to show that determination of the time at which the PU-loop first deviates from linearity provides a convenient way to determine the arrival time of reflected waves (Tr). We also present a new technique using the PU-loop that allows for the determination of wave speed and Tr simultaneously. We measured pressure and flow in elastic tubes of different diameters, where a strong reflection site existed at known distances away form the measurement site. We also measured pressure and flow in the ascending aorta of 11 anaesthetised dogs where a strong reflection site was produced through total arterial occlusion at four different sites. Wave speed was determined from the initial slope of the PU-loop and Tr was determined using a new algorithm that detects the sampling point at which the initial linear part of the PU-loop deviates from linearity. The results of the new technique for detecting Tr were comparable to those determined using the foot-to-foot and wave intensity analysis methods. In elastic tubes Tr detected using the new algorithm was almost identical to that detected using wave intensity analysis and foot-to-foot methods with a maximum difference of 2%. Tr detected using the PU-loop in vivo highly correlated with that detected using wave intensity analysis (r 2 = 0.83, P < 0.001). We conclude that the new technique described in this paper offers a convenient and objective method for detecting Tr, and allows for the dynamic determination of wave speed and Tr, simultaneously

3D printed electro-responsive system with programmable drug release

Precision medicine is the next frontier in pharmaceutical research, aiming to improve the safety and efficacy of therapeutics for patients. The ideal drug delivery system (DDS) should be programmable to provide real-time controlled delivery that is personalised to the patient's needs. However, little progress has been made in this domain. Herein, we combined two cutting-edge technologies, conductive polymers (CPs) and three-dimensional (3D) printing, to demonstrate their potential for achieving programmable controlled release. A DDS was formulated where the CP provided temporal control over drug release. 3D printing was used to ensure dimensional control over the design of the DDS. The CP used in this study is known to be fragile, and thus was blended with thermoplastic polyurethane (TPU) to achieve a conductive elastomer with sound mechanical properties. Rheological and mechanical analyses were performed, where it was revealed that formulation inks with a storage modulus in the order of 103–104 Pa were both extrudable and maintained their structural integrity. Physico-chemical analysis confirmed the presence of the CP functional groups in the 3D printed DDS. Cyclic voltammetry demonstrated that the DDS remained conductive for 100 stimulations. in vitro drug release was performed for 180 min at varying voltages, where a significant difference (p < 0.05) in cumulative release was observed between either ±1.0 V and passive release. Furthermore, the responsiveness of the DDS to pulsatile stimuli was tested, where it was found to rapidly respond to the voltage stimuli, consequently altering the release mechanism. The study is the first to 3D print electroactive medicines using CPs and paves the way for digitalising DDS that can be integrated into the Internet of Things (IoT) framework

Cvar-Based Robust Models For Portfolio Selection

This study relaxes the distributional assumption of the return of the risky asset, to arrive at the optimal portfolio. Studies of portfolio selection models have typically assumed that stock returns conform to the normal distribution. The application of robust optimization techniques means that only the historical mean and variance of asset returns are required instead of distributional information. We show that the method results in an optimal portfolio that has comparable return and yet equivalent risk, to one that assumes normality of asset returns

The Benefit of Enhanced Contractility in the Infarct Borderzone: A Virtual Experiment

Objectives: Contractile function in the normally perfused infarct borderzone (BZ) is depressed. However, the impact of reduced BZ contractility on left ventricular (LV) pump function is unknown. As a consequence, there have been no therapies specifically designed to improve BZ contractility. We tested the hypothesis that an improvement in borderzone contractility will improve LV pump function. Methods: From a previously reported study, magnetic resonance imaging (MRI) images with non-invasive tags were used to calculate 3D myocardial strain in five sheep 16 weeks after anteroapical myocardial infarction. Animal-specific finite element (FE) models were created using MRI data and LV pressure obtained at early diastolic filling. Analysis of borderzone function using those FE models has been previously reported. Chamber stiffness, pump function (Starling’s law) and stress in the fiber, cross fiber, and circumferential directions were calculated. Animal-specific FE models were performed for three cases: (a) impaired BZ contractility (INJURED); (b) BZ-contractility fully restored (100% BZ IMPROVEMENT); or (c) BZ-contractility partially restored (50% BZ IMPROVEMENT). Results: 100% BZ IMPROVEMENT and 50% BZ IMPROVEMENT both caused an upward shift in the Starling relationship, resulting in a large (36 and 26%) increase in stroke volume at LVPED = 20 mmHg (8.0 ml, p < 0.001). Moreover, there were a leftward shift in the end-systolic pressure volume relationship, resulting in a 7 and 5% increase in LVPES at 110 mmHg (7.7 ml, p < 0.005). It showed that even 50% BZ IMPROVEMENT was sufficient to drive much of the calculated increase in function. Conclusion: Improved borderzone contractility has a beneficial effect on LV pump function. Partial improvement of borderzone contractility was sufficient to drive much of the calculated increase in function. Therapies specifically designed to improve borderzone contractility should be developed

Myonuclear accretion is a determinant of exercise-induced remodeling in skeletal muscle.

Skeletal muscle adapts to external stimuli such as increased work. Muscle progenitors (MPs) control muscle repair due to severe damage, but the role of MP fusion and associated myonuclear accretion during exercise are unclear. While we previously demonstrated that MP fusion is required for growth using a supra-physiological model (Goh and Millay, 2017), questions remained about the need for myonuclear accrual during muscle adaptation in a physiological setting. Here, we developed an 8 week high-intensity interval training (HIIT) protocol and assessed the importance of MP fusion. In 8 month-old mice, HIIT led to progressive myonuclear accretion throughout the protocol, and functional muscle hypertrophy. Abrogation of MP fusion at the onset of HIIT resulted in exercise intolerance and fibrosis. In contrast, ablation of MP fusion 4 weeks into HIIT, preserved exercise tolerance but attenuated hypertrophy. We conclude that myonuclear accretion is required for different facets of exercise-induced adaptive responses, impacting both muscle repair and hypertrophic growth

Topics on global analysis of manifolds and representation theory of reductive groups

Geometric symmetry induces symmetries of function spaces, and the latter yields a clue to global analysis via representation theory. In this note we summarize recent developments on the general theory about how geometric conditions affect representation theoretic properties on function spaces, with focus on multiplicities and spectrum.Comment: 14 page