A 1D pulse wave propagation model of the hemodynamics of calf muscle pump function

The calf muscle pump is a mechanism which increases venous return and thereby compensates for the fluid shift towards the lower body during standing. During a muscle contraction, the embedded deep veins collapse and venous return increases. In the subsequent relaxation phase, muscle perfusion increases due to increased perfusion pressure, as the proximal venous valves temporarily reduce the distal venous pressure (shielding). The superficial and deep veins are connected via perforators, which contain valves allowing flow in the superficial-to-deep direction. The aim of this study is to investigate and quantify the physiological mechanisms of the calf muscle pump, including the effect of venous valves, hydrostatic pressure, and the superficial venous system. Using a one-dimensional pulse wave propagation model, a muscle contraction is simulated by increasing the extravascular pressure in the deep venous segments. The hemodynamics are studied in three different configurations: a single artery–vein configuration with and without valves and a more detailed configuration including a superficial vein. Proximal venous valves increase effective venous return by 53% by preventing reflux. Furthermore, the proximal valves shielding function increases perfusion following contraction. Finally, the superficial system aids in maintaining the perfusion during the contraction phase and reduces the refilling time by 37%

Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal and cubic phases of methylammonium lead iodide

The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behaviour, with successive transitions between orthorhombic, tetragonal and cubic polymorphs at ca. 165 K and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of the sample. Despite a clear separation in energy between low frequency modes associated with the inorganic PbI3 network and high-frequency modes of the organic CH3NH3+ cation, significant coupling between them is found, which emphasises the interplay between molecular orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI6 octahedra around room temperature.Comment: 9 pages, 4 figure

Does dehydration alter the success rate and technique of three-point shooting in elite basketball?

In order to better inform the effects of dehydration and hydration guidelines, we tested the acute effects of a 2% dehydration protocol on performance and technique of 3-point shooting (3PS) in Elite Basketball players (n = 9). The 3PS technique was monitored by using nanotechnology inertial measurement units positioned onto body joints during the exercise. When dehydrated (−2.1% ± 0.5% of body mass), 7 players experienced a slight decrease (−10.0% ± 19.6%, p = 0.16) in success rate, while RPE increased from 9.1 ± 2.6 to 13.0 ± 2.5 in euhydrated (EUH) and dehydrated (DEH) condition respectively (p = 0.003). DEH slightly altered the 3PS technique as the knee angle increased (p = 0.02) at toe-off time and the hip angle decreased during the 3PS (p = 0.01). The speed of ball release tended to be increased (p = 0.05) in DEH compared to EUH. Data from this study suggest that a 2% dehydration is tolerable for elite Basketball players, although a stronger dehydration might accentuate the effects observed

Effect of dehydration on performance and technique of three-point shooting in Elite Basketball.

Basketball play is classically accompanied with a significant loss of body water with a potential negative impact on both physical and cognitive performance 1. Very few studies have examined the impact of dehydration on biomechanical adjustments required to score in basketball, though joints angles, the position of the centre of mass and ball release parameters (i.e. height, release speed and angle) are among the best predictive factors of success in basketball shooting 2. Dehydration might alter the biomechanical requirements of successful shots and especially three-point shots (3PS) which generate 16% of points scored during a match. However, only 35% of 3PS are successful in game. Within this framework we analysed the effects of a controlled dehydration protocol on the success and technique of 3PS in elite basketball players. Changes in shooting technique were analysed through changes in body kinematics (i.e. 3D angles of the ankle, knee, hip, shoulder, elbow and wrist, and the height of the centre of mass) and ball release parameters (i.e. height, velocity and angle of the ball at release) of 3PS in a dynamic playing condition

The dynamics of methylammonium ions in hybrid organic-inorganic perovskite solar cells

Methylammonium lead iodide perovskite can make high-efficiency solar cells, which also show an unexplained photocurrent hysteresis dependent on the device-poling history. Here we report quasielastic neutron scattering measurements showing that dipolar CH3NH3+ ions reorientate between the faces, corners or edges of the pseudo-cubic lattice cages in CH3NH3PbI3 crystals with a room temperature residence time of ~14 ps. Free rotation, π-flips and ionic diffusion are ruled out within a 1–200-ps time window. Monte Carlo simulations of interacting CH3NH3+ dipoles realigning within a 3D lattice suggest that the scattering measurements may be explained by the stabilization of CH3NH3+ in either antiferroelectric or ferroelectric domains. Collective realignment of CH3NH3+ to screen a device’s built-in potential could reduce photovoltaic performance. However, we estimate the timescale for a domain wall to traverse a typical device to be ~0.1–1 ms, faster than most observed hysteresis

Modelling regulation of vascular tone following muscle contraction: model development, validation and global sensitivity analysis

In this study the regulation of vascular tone inducing the blood flow increase at the onset of exercise is examined. Therefore, our calf circulation model was extended with a regulation model to simulate changes in vascular tone depending on myogenic, metabolic and baroreflex regulation. The simulated blood flow corresponded to the in vivo response and it was concluded that metabolic activation caused the flow increase shortly after muscle contraction. Secondly, the change in baseline flow upon tilt was a result of myogenic and baroreflex activation. Based on a sensitivity analysis the myogenic gain was identified as most important parameter

Reversible hydration of CH(3)NH(3)Pbl(3) in films, single crystals, and solar cells

Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that (i) hydrated crystal phases are formed when MAPI is exposed to water vapor at room temperature and (ii) these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was observed using time-resolved XRD and ellipsometry of thin films prepared using “solvent engineering”, single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH3NH3PbI3·H2O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single-crystal optical constants and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were modeled. The results suggest that the monohydrate phase forms independent of the depth in the film, suggesting rapid transport of water molecules along grain boundaries. Vapor-phase hydration of an unencapsulated solar cell (initially Jsc ≈ 19 mA cm–2 and Voc ≈ 1.05 V at 1 sun) resulted in more than a 90% drop in short-circuit photocurrent and ∼200 mV loss in open-circuit potential; however, these losses were fully reversed after the device was exposed to dry nitrogen for 6 h. Hysteresis in the current–voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect density and morphology of MAPI following recrystallization from the hydrate. Based on our observations, we suggest that irreversible decomposition of MAPI in the presence of water vapor only occurs significantly once a grain has been fully converted to the monohydrate phase

Experimental and theoretical optical properties of methylammonium lead halide perovskites

The optical constants from the ellipsometry of single crystals of CH3NH3PbX3(X = I, Br, Cl) are interpreted with high levelab initioQSGW calculations.</p

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions - notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods - taking a secondary role. © 2020 Wolters Kluwer Medknow Publications. All rights reserved