Galilean-Invariant Characteristic-Based Volume Penalization Method for Supersonic Flows with Moving Boundaries

This work extends the characteristic-based volume penalization method, originally developed and demonstrated for compressible subsonic viscous flows in (J. Comput. Phys. 262, 2014), to a hyperbolic system of partial differential equations involving complex domains with moving boundaries. The proposed methodology is shown to be Galilean-invariant and can be used to impose either homogeneous or inhomogeneous Dirichlet, Neumann, and Robin type boundary conditions on immersed boundaries. Both integrated and non-integrated variables can be treated in a systematic manner that parallels the prescription of exact boundary conditions with the approximation error rigorously controlled through an a priori penalization parameter. The proposed approach is well suited for use with adaptive mesh refinement, which allows adequate resolution of the geometry without over-resolving flow structures and minimizing the number of grid points inside the solid obstacle. The extended Galilean-invariant characteristic-based volume penalization method, while being generally applicable to both compressible Navier–Stokes and Euler equations across all speed regimes, is demonstrated for a number of supersonic benchmark flows around both stationary and moving obstacles of arbitrary shape.

RHEOLOGICAL PROPERTIES OF MIXTURES OF RANDOM POLYPROPYLENE WITH BUTADIENE-NITRILE RUBBER AND VULCANIZATES BASED ON THEM

The paper presents the results of studying the effects of butadiene-nitrile rubber concentration and temperature on the flow curves of the random polypropylene-based polymer blends. To improve the technological compatibility of polymer blends, a graft(ed) copolymer of polypropylene with maleic anhydride was used as a compatibilizer. Melt viscosity as a function of temperature and shear rate is shown, and the activation energy of a viscous flow has been defined. A generalized temperature-invariant characteristic of the viscosity properties of polymer blends has been plotted. This makes it possible to predict the value of their effective viscosity at high shear rates, close to real processing conditions

Rheological properties of organo-inorganic hybrid gels based on functionalized low density polyethylene and clinoptilolite

The results of studying the effect of temperature on the dependence of shear rate on shear stress, effective viscosity on shear rate and effective viscosity on reciprocal temperature in Arrhenius coordinates for nanocomposites based on chemically modified low density polyethylene and clinoptilolite are presented. The object of study was the initial polyethylene functionalized with methacrylic acid filled with clinoptilolite, as well as hybrid gels based on modified polyethylene filled with appreted clinoptilolite. A temperature-invariant characteristic of the viscosity properties of hybrid gels is constructed, which allows predicting the temperature regime of their processing by injection molding and extrusion.

Observed Relationship between Tornado Intensity and Pretornadic Mesocyclone Characteristics

In a previous study, idealized model simulations of supercell thunderstorms were used to demonstrate support of the hypothesis that wide, intense tornadoes should form more readily out of wide, rotating updrafts. Observational data were used herein to test the generality of this hypothesis, especially to tornado-bearing convective morphologies such as quasi-linear convective systems (QLCSs), and within environments such as those found in the southeastern United States during boreal spring and autumn. A new radar dataset was assembled that focuses explicitly on the pretornadic characteristics of the mesocyclone, such as width and differential velocity: the pretornadic focus allows us to eliminate the effects of the tornado itself on the mesocyclone characteristics. GR2Analyst was used to manually analyze 102 tornadic events during the period 27 April 2011–1 May 2019. The corresponding tornadoes had damage (EF) ratings ranging from EF0 to EF5, and all were within 100 km of a WSR-88D. A key finding is that the linear regression between the mean, pretornadic mesocyclone width and the EF rating of the corresponding tornado yields a coefficient of determination (R2) value of 0.75. This linear relationship is higher for discrete (supercell) cases (R2 = 0.82), and lower for QLCS cases (R2 = 0.37). Overall, we have found that pretornadic mesocyclone width tends to be a persistent, relatively time-invariant characteristic that is a good predictor of potential tornado intensity. In contrast, the pretornadic mesocyclone intensity (differential velocity) tends to exhibit considerable time variability, and thus would offer less reliability in anticipating tornado intensity.

COMPaRS: a stand-alone program for map comparison using quantile rank scaling

The usual metrics for comparison of two crystallographic or cryoEM maps, for example the overall map correlation coefficient, measure the similarity of two sets of values with no consideration of their position in space. In contrast, when analyzing the maps visually it is the positions of sets of points with map values equal to or greater than some cutoff level that is of interest. An intrinsic and scale-invariant characteristic of such a set is the quantile rank defining the fraction of grid nodes (or of the unit-cell volume) with values less than this cutoff level. Comparison of the quantile ranks associated with the same point in the two maps is very similar to a comparison of the isosurfaces. The programCOMPaRSuses new metrics for map comparison based on this idea: this gives quantitative results that agree with the qualitative results obtained from a visual analysis.

Should the Equilibrium Point Hypothesis (EPH) Be Considered a Scientific Theory?

The purpose of this commentary is to discuss factors that limit consideration of the equilibrium point hypothesis as a scientific theory. The EPH describes control of motor neuron threshold through the variable lambda, which corresponds to a unique referent configuration for a muscle, joint, or combination of joints. One of the most compelling features of the equilibrium point hypothesis is the integration of posture and movement control into a single mechanism. While the essential core of the hypothesis is based upon spinal circuitry interacting with peripheral mechanics, the proponents have extended the theory to include the higher-level processes that generate lambda, and in doing so, imposed an injunction against the supraspinal nervous system modeling, computing, or predicting dynamics. This limitation contradicts evidence that humans take account of body and environmental dynamics in motor selection, motor control, and motor adaptation processes. A number of unresolved limitations to the EPH have been debated in the literature for many years, including whether muscle resistance to displacement, measured during movement, is adequate to support this form of control, violations in equifinality predictions, spinal circuits that alter the proposed invariant characteristic for muscles, and limitations in the description of how the complexity of spinal circuitry might be integrated to yield a unique and stable equilibrium position for a given motor neuron threshold. In addition, an important empirical limitation of EPH is the measurement of the invariant characteristic, which needs to be done under a constant central state. While there is no question that the EPH is an elegant and generative hypothesis for motor control research, the claim that this hypothesis has reached the status of a scientific theory is premature.