Institutionalized elderly are able to detect small viscosity variations in thickened water with gum-based thickeners: should texture classifications be reviewed?

Background The prevalence of dysphagia is very high in institutionalized elderly. Knowledge of the rheological and sensory characteristics of the various thickeners in elderly is limited, although it has been seen that there are differences between the rheological behaviors of gum-based thickeners with different composition. Moreover, we have not found sensory studies of viscosity in institutionalized elderly. Our hypothesis was that viscosity ranges established by the scientific societies, such as the National Dysphagia Diet Task Force (NDD), seem to be very wide and individuals might be able to detect small differences within the same texture range. The objectives of our study were 1) comparing the rheological characteristics of two commercial gum-based thickeners with different composition, dissolved in water under standard conditions, and 2) perform a sensory analysis (with both adults and institutionalized elderly) to detect different viscosities within the same texture (nectar and honey). Methods Two commercial thickeners based on gums (NC and RC) were studied analyzing their viscosity in water with different concentrations (shear rate: 50 s− 1; temperature: 22–25 °C). A sensory analysis involving 26 elderly and 29 adult controls was carried out to evaluate whether differences within nectar and honey textures among gum-based thickeners could be distinguished. Results As the shear rate increases, viscosity decreases (non-Newtonian and pseudoplastic behavior). At the same concentration, each thickener produces a different viscosity (p < 0.05). Institutionalized elderly detected viscosity differences in nectar range of 49.9 (2.5) mPa·s (p < 0.05) and 102.2 (4.7) mPa·s (p < 0.0001). They also detected viscosity differences in honey texture range of 134.6 (9.7) mPa·s (p < 0.05) y 199.3 (9.2) mPa·s (p < 0.0001). Their caregivers also detected viscosity differences in both viscosity ranges (p < 0.0001) and with greater intensity than the elderly in honey texture (p: 0.016). Conclusions Our results suggest that the accepted viscosity ranges by NDD for the different textures might be too wide because institutionalized elderly and their caregivers are able to discern small differences in viscosity in nectar and honey textures. Gum-based thickeners with different composition showed differences in viscosity capacity, so they are not interchangeable.

Proof of the zeroth law of turbulence in one-dimensional compressible magnetohydrodynamics and heating of the sawtooth solar wind

&lt;p&gt;The zeroth law of turbulence is one of the oldest conjecture in turbulence that is still unproven. We consider weak solutions of one-dimensional (1D) compressible magnetohydrodynamics (MHD) and demonstrate that the lack of smoothness of the fields introduces a new dissipative term, named inertial dissipation, into the expression of energy conservation that is neither viscous nor resistive in nature. We propose exact solutions assuming that the kinematic viscosity and the magnetic diffusivity are equal, and we demonstrate that the associated inertial dissipation is, on average, positive and equal to the&amp;#160;mean viscous dissipation rate in the limit of small viscosity, proving the conjecture of the zeroth law of turbulence.&lt;/p&gt;&lt;p&gt;We show that discontinuities commonly de- tected by Voyager 1 &amp; 2 in the solar wind at 2&amp;#8211;10AU can be fitted by the inviscid analytical profiles. We deduce a heating rate of &amp;#8764; 10&lt;sup&gt;&amp;#8722;18&lt;/sup&gt; Jm&lt;sup&gt;&amp;#8722;3&lt;/sup&gt;s&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; , which is significantly higher than the value obtained from the turbulent fluctuations. This suggests that collisionless shocks are a dominant source of heating in the outer solar wind.&lt;/p&gt;

Institutionalized Elderly are able to Detect Small Viscosity Variations in Thickened Water with Gum-based Thickeners. Should Texture Classifications be Reviewed?

Background: The prevalence of dysphagia is very high in institutionalized elderly. Knowledge of the rheological and sensory characteristics of the various thickeners is limited, although it has been seen that there are differences between the rheological behaviors of different gum-based thickeners with different composition. We have not found sensory studies of viscosity in institutionalized elderly. Our hypothesis was that viscosity ranges established by the scientific societies seem to be very wide and individuals might be able to detect small differences within the same texture range. The objectives of our study were comparing the rheological characteristics of two commercial gum-based thickeners with different composition, dissolved in water under standard conditions, and checking whether it could be possible to detect different viscosities within the same texture (nectar and honey) with the use of sensory analysis (both with adults and elderly). Methods: Two commercial thickeners based on gums (NC and RC) were studied analyzing their viscosity in water with different concentrations (shear rate: 50 s-1; temperature: 22-25°C). A sensory analysis involving 26 elderly and 29 adult controls was carried out to evaluate whether differences within nectar and honey textures among gum-based thickeners could be distinguished. Results: As the shear rate increases, viscosity decreases (non-Newtonian and pseudoplastic behavior). At the same concentration, each thickener produces a different viscosity (p<0.05). Institutionalized elderly detected viscosity differences in nectar range of 49.9 (2.5) mPa·s (p<0.05) y 102.2 (4.7) mPa·s (p<0.0001). They also detected viscosity differences in honey texture range of 134.6 (9.7) mPa·s (p<0.05) y 199,3 (9,2) mPa·s (p<0.0001). Their caregivers also detected viscosity differences in both viscosity ranges (p<0.0001). Conclusions: Our results suggest that the accepted viscosity ranges for the different textures might be too wide because institutionalized elderly and their caregivers are able to discern small differences in viscosity in nectar and honey textures. Gum-based thickeners with different composition showed differences in viscosity capacity, so they are not interchangeable.

Propagating fronts for a viscous Hamer-type system

<p style='text-indent:20px;'>Motivated by radiation hydrodynamics, we analyse a <inline-formula><tex-math id="M1">\begin{document}$ 2\times2 $\end{document}</tex-math></inline-formula> system consisting of a one-dimensional viscous conservation law with strictly convex flux –the viscous Burgers' equation being a paradigmatic example– coupled with an elliptic equation, named <b>viscous Hamer-type system</b>. In the regime of small viscosity and for large shocks, namely when the profile of the corresponding underlying inviscid model undergoes a discontinuity –usually called <i>sub-shock</i>– it is proved the existence of a smooth propagating front, regularising the jump of the corresponding inviscid equation. The proof is based on <i>Geometric Singular Perturbation Theory</i> (GSPT) as introduced in the pioneering work of Fenichel [<xref ref-type="bibr" rid="b5">5</xref>] and subsequently developed by Szmolyan [<xref ref-type="bibr" rid="b21">21</xref>]. In addition, the case of small shocks and large viscosity is also addressed via a standard bifurcation argument.</p>

Dynamical transitions during the collapse of inertial holes

At the center of a collapsing hole lies a singularity, a point of infinite curvature where the governing equations break down. It is a topic of fundamental physical interest to clarify the dynamics of fluids approaching such singularities. Here, we use scaling arguments supported by high-fidelity simulations to analyze the dynamics of an axisymmetric hole undergoing capillary collapse in a fluid sheet of small viscosity. We characterize the transitions between the different dynamical regimes —from the initial inviscid dynamics that dominate the collapse at early times to the final Stokes dynamics that dominate near the singularity— and demonstrate that the crossover hole radii for these transitions are related to the fluid viscosity by power-law relationships. The findings have practical implications for the integrity of perforated fluid films, such as bubble films and biological membranes, as well as fundamental implications for the physics of fluids converging to a singularity.