Regional mantle viscosity constraints for North America reveal upper mantle strength differences across the continent

We present regional constraints of mantle viscosity for North America using a local Bayesian joint inversion of mantle flow and glacial isostatic adjustment (GIA) models. Our localized mantle flow model uses new local geoid kernels created via spatio-spectral localization using Slepain basis functions, convolved with seismically derived mantle density to calculate and constrain against the regional free-air gravity field. The joint inversion with GIA uses two deglaciation of ice sheet models (GLAC1D-NA and ICE-6G-NA) and surface relative sea level data. We solve for the local 1D mantle viscosity structure for the entire North America (NA) region, the eastern region including Hudson Bay, and the western region of North America extending into the Pacific plate. Our results for the entire NA region show one order of magnitude viscosity jump at the 670 km boundary using a high seismic density scaling parameter (e.g., δlnp/δlnvs = 0.3). Seismic scaling parameter demonstrates significant influence on the resulting viscosity profile. However, when the NA region is further localized into eastern and western parts, the scaling factor becomes much less important for dictating the resulting upper mantle viscosity characteristics. Rather the respective local mantle density heterogeneities provide the dominate control on the upper mantle viscosity. We infer local 1D viscosity profiles that reflect the respective tectonic settings of each region's upper mantle, including a weak and shallow asthenosphere layer in the west, and deep sharp viscosity jumps in the eastern transition zone, below the suggested/proposed depth range of the eastern continental root.

Molecular Modelling of Ionic Liquids: Force-Field Validation and Thermodynamic Perspective from Large-Scale Fast-Growth Solvation Free Energy Calculations

Molecular simulations are becoming a common tool for the investigation of dynamic and thermodynamic properties of novel solvents such as ionic liquids and the more recent deep eutectic solvents. As the electrostatics derived from ab initio calculations often fail to reproduce the experimental behaviors of these functionalized solvents, a common treatment is scaling the atomic charges to improve the accord between experimental and computational results for some selected properties, e.g., the density of the liquids. Although there are many computational benchmarks on structural properties of bulk ionic liquids, the choice of the best scaling parameter remains an open question. As these liquids are designed to solvate solutes, whether the solvation thermodynamics could be correctly described is of utmost importance in practical situations. Therefore, in the current work, we provide a thermodynamic perspective of this charge scaling issue directly from solute-solvent interactions. We present a comprehensive large-scale calculation of solvation free energies via nonequilibrium fast-switching simulations for a spectrum of molecules in ionic liquids, the atomic charges of which derived from ab initio calculations are scaled to find the best scaling factor that maximizes the prediction-experiment correlation. The density-derived choice of the scaling parameter as the estimate from bulk properties is compared with the solvation-free-energy-derived one. We observed that when the scaling factor is decreased from 1.0 to 0.5, the mass density exhibits a monotonically decreasing behavior, which is caused by weaker inter-molecular interactions produced by the scaled atomic charges. However, the solvation free energies of external agents do not show consistent monotonic behaviors like the bulk property, the underlying physics of which are elucidated to be the competing electrostatic and vdW responses to the scaling-parameter variation. More intriguingly, although the recommended value for charge scaling from bulk properties falls in the neighborhood of 0.6~0.7, solvation free energies calculated at this value are not in good agreement with the experimental reference. By modestly increasing the scaling parameter (e.g., by 0.1) to avoid over-scaling of atomic charges, the solute-solvent interaction free energy approaches the reference value and the quality of calculated solvation thermodynamics approaches the hydration case. According to this phenomenon, we propose a feasible way to obtain the best scaling parameter that produces balanced solute-solvent and solvent-solvent interactions, i.e., first scanning the density-scaling-factor profile and then adding ~0.1 to that solution. We further calculate the partition coefficient or transfer free energy of solutes from water to ionic liquids to provide another thermodynamic perspective of the charge scaling benchmark. Another central result of the current work is about the widely used force fields to describe bonded and vdW terms for ionic liquids derivatives. These pre-fitted transferable parameters are evaluated and refitted in a system-specific manner to provide a detailed assessment of the reliability and accuracy of these commonly used parameters. Component-specific refitting procedures unveil that the bond-stretching term is the most problematic part of the GAFF derivatives and the angle-bending term in some cases is also not accurate enough. Astonishingly, the torsional potential defined in these pre-fitted force fields performs extremely well.

Change in the amplitude of strong discontinuity wave propagating in a rod made of Murnaghan material

The paper presents calculations of the change in amplitude of strong discontinuity wave propagating in a thin rod made of hyperelastic Murnaghan material. Two functions were assumed for the calculations, describing the change of the cross-section of the rod with the constant scaling parameter?for both decreasing cross-sections of the analysed steel rods. A numerical analysis was performed based on analytical solutions. The analytical form of solution for both rods with decreasing cross-sections allowed for preparation of contour maps for the propagating wave of strong discontinuity. Furthermore, the changes in the relative amplitude of the propagating shock wave in a thin rod were determined for two rods analysed in the study, for which the differences in the values of the relative amplitude in the final cross-section were found.

Reinforcer Quality and Self-Control

<p>Self-control has been extensively studied using procedures in which subjects chose between two reinforcer alternatives. Traditionally, one of those alternatives delivers a small reinforcer after a short delay (SI), the other, a larger reinforcer after a long delay (LD). Choosing the SI is defined as impulsivity as it requires forfeit of the larger reinforcer; and choosing the LD is termed self-control. Four experiments were conducted to examine behaviour using non-human animal analogues of self-control situations. The subjects used for all four experiments were Norway-hooded rats. Experiment 1 used an SI - LD self-control paradigm to examine the effect of manipulating reinforcer quality on response distribution. Findings were that behaviour became more impulsive as the delay ratio became more extreme and this tendency was more systematic when different quality reinforcers were used for the SI and LD alternatives. Experiments 2 and 3 introduced a novel self-control paradigm designed as an analogue of choice situations in which individuals choose between two competing immediately available reinforcers each associated with a different delayed reinforcer. The procedure used was a concurrent-chains schedule that delivered primary reinforcement in the initial and the terminal links. The initial reinforcers were of equal amount and unequal quality; the terminal reinforcers were of unequal amount and equal quality. An impulsive choice was defined as choosing the alternative that delivered the most-valuable reinforcer in the initial link and the least-valued reinforcer in the terminal link. A self-controlled choice was defined as choosing the alternative that delivered the least-valuable reinforcer in the initial link and the most-valuable reinforcer in the terminal link. The results indicated that behaviour was more self-controlled when the terminal reinforcer quality was ethanol solution and increasing the delay between the initial and terminal links increased subjects' responding on the impulsive choice. Behaviour allocation in Experiment 3 was well described by the Contextual Choice Model (Grace, 1994) when the temporal context scaling parameter (k) was allowed to vary. Subjects that were relatively more impulsive had lower derived k values. The final experiment presented the subjects from Experiment 3 with concurrent variable interval (VI) VI schedules in which one alternative delivered plain-sucrose solution and the other ethanol-sucrose solution. Preference measures obtained from Experiment 4 were negatively correlated with the values obtained for the scaling parameter in Experiment 3, indicating that subjects which were more impulsive in the MN - ML paradigm had a stronger preference for ethanol. In summary, findings indicate that reinforcer quality may change the discriminability of reinforcer alternatives; and the influence of reinforcer quality on response allocation is well described by quantitative models based on the Matching Law.</p>

Reinforcer Quality and Self-Control

<p>Self-control has been extensively studied using procedures in which subjects chose between two reinforcer alternatives. Traditionally, one of those alternatives delivers a small reinforcer after a short delay (SI), the other, a larger reinforcer after a long delay (LD). Choosing the SI is defined as impulsivity as it requires forfeit of the larger reinforcer; and choosing the LD is termed self-control. Four experiments were conducted to examine behaviour using non-human animal analogues of self-control situations. The subjects used for all four experiments were Norway-hooded rats. Experiment 1 used an SI - LD self-control paradigm to examine the effect of manipulating reinforcer quality on response distribution. Findings were that behaviour became more impulsive as the delay ratio became more extreme and this tendency was more systematic when different quality reinforcers were used for the SI and LD alternatives. Experiments 2 and 3 introduced a novel self-control paradigm designed as an analogue of choice situations in which individuals choose between two competing immediately available reinforcers each associated with a different delayed reinforcer. The procedure used was a concurrent-chains schedule that delivered primary reinforcement in the initial and the terminal links. The initial reinforcers were of equal amount and unequal quality; the terminal reinforcers were of unequal amount and equal quality. An impulsive choice was defined as choosing the alternative that delivered the most-valuable reinforcer in the initial link and the least-valued reinforcer in the terminal link. A self-controlled choice was defined as choosing the alternative that delivered the least-valuable reinforcer in the initial link and the most-valuable reinforcer in the terminal link. The results indicated that behaviour was more self-controlled when the terminal reinforcer quality was ethanol solution and increasing the delay between the initial and terminal links increased subjects' responding on the impulsive choice. Behaviour allocation in Experiment 3 was well described by the Contextual Choice Model (Grace, 1994) when the temporal context scaling parameter (k) was allowed to vary. Subjects that were relatively more impulsive had lower derived k values. The final experiment presented the subjects from Experiment 3 with concurrent variable interval (VI) VI schedules in which one alternative delivered plain-sucrose solution and the other ethanol-sucrose solution. Preference measures obtained from Experiment 4 were negatively correlated with the values obtained for the scaling parameter in Experiment 3, indicating that subjects which were more impulsive in the MN - ML paradigm had a stronger preference for ethanol. In summary, findings indicate that reinforcer quality may change the discriminability of reinforcer alternatives; and the influence of reinforcer quality on response allocation is well described by quantitative models based on the Matching Law.</p>

Diversity Scaling of Human Digestive Tract (DT) Microbiomes: The Intra-DT and Inter-individual Patterns

The human gut microbiome has been extensively studied, but its diversity scaling (changes or heterogeneities) along the digestive tract (DT) as well as their inter-individual heterogeneities have not been adequately addressed to the best of our knowledge. Here we fill the gap by applying the diversity-area relationship (DAR), a recent extension to the classic species-area relationship (SAR) in biogeography, by reanalyzing a dataset of over 2000 16s-rRNA microbiome samples obtained from 10 DT sites of over 200 individuals. We sketched out the biogeography “maps” for each of the 10 DT sites by cross-individual DAR analysis, and the intra-DT distribution pattern by cross-DT-site DAR analysis. Regarding the inter-individual biogeography, it was found that all DT sites have the invariant (constant) scaling parameter—all sites possessing the same diversity change rate across individuals, but most sites have different potential diversities, which include the portions of diversity that may be absent locally but present regionally. In the case of this study, the potential diversity of each DT site covers the total diversity of the respective site from all individuals in the cohort. In terms of the genus richness, an average individual hosts approximately 20% of the population-level genus richness (total bacterial genus of a human population). In contrast, in terms of community biodiversity, the percentages of individual over population may exceed 90%. This suggests that the differences between individuals in their DT microbiomes are predominantly in the composition of bacterial species, rather than how their abundances are distributed (i.e., biodiversity). Regarding the intra-DT patterns, the scaling parameter (z) is larger—suggesting that the intra-DT biodiversity changes are larger than inter-individual changes. The higher intra-DT heterogeneity of bacteria diversity, as suggested by larger intra-DT z than the inter-individual heterogeneity, should be expected since the intra-DT heterogeneity reflects the functional differentiations of the DT tract, while the inter-individual heterogeneity (z) reflects the difference of the same DT site across individuals. On average, each DT site contains 21–36% of the genus diversity of the whole DT, and the percentages are even higher in terms of higher taxon levels.

Explicit comprehensive models for single ring infiltration: suggestions for model application and parameterization

&lt;p&gt;Stewart and Abou Najm (2018) developed a comprehensive model (SA model) for single ring infiltration that consists of a couple of two-terms explicit infiltration equations similar, in form, to the approximate expansions proposed by Haverkamp et al. (1994) (HV model). Application of SA model requires the transition time, &amp;#964;&lt;sub&gt;crit&lt;/sub&gt;, from transient to steady state to be known &lt;em&gt;a-priori&lt;/em&gt; or establishing a constraint among the four constants that figure in the infiltration equations. Estimation of soil saturated hydraulic conductivity, &lt;em&gt;K&lt;sub&gt;s&lt;/sub&gt;&lt;/em&gt;, and capillary length, &amp;#955;, from single ring infiltration measurements also needs a scaling parameter referred to &amp;#8220;&lt;em&gt;a&lt;/em&gt;&amp;#8221; to be known. SA model assumes this scaling parameter as a constant and fixes its value at &lt;em&gt;a&lt;/em&gt; = 0.45. However, there is evidence that &lt;em&gt;a&lt;/em&gt; cannot be considered a constant independent of soil type and initial water content.&lt;/p&gt;&lt;p&gt;This study investigates some open issues related to the use of the SA model for single ring infiltration: 1) how comparable is &amp;#964;&lt;sub&gt;crit&lt;/sub&gt; with the maximum time, &lt;em&gt;t&lt;/em&gt;&lt;sub&gt;max&lt;/sub&gt;, that separates transient from steady state condition in HV model; 2) how the scaling parameter &lt;em&gt;a&lt;/em&gt; depends on different experimental conditions and how it can be related to HV parameters.&lt;/p&gt;&lt;p&gt;Preliminary theoretical considerations showed that the two characteristic times (&amp;#964;&lt;sub&gt;crit&lt;/sub&gt; and &lt;em&gt;t&lt;/em&gt;&lt;sub&gt;max&lt;/sub&gt;) are related and, for relatively dry initial conditions, parameter &lt;em&gt;a&lt;/em&gt; depends only on the soil type and ring radius being maximum for small ring radii or soils with high capillarity (&lt;em&gt;a&lt;/em&gt; = 1) and minimum for large rings or coarse soils (&lt;em&gt;a&lt;/em&gt; = 0.467).&lt;/p&gt;&lt;p&gt;An optimization procedure, with a constraint among the four infiltration constants, was applied to fit the SA model to both analytical and experimental infiltration data to derive&amp;#160; &amp;#964;&lt;sub&gt;crit&lt;/sub&gt; and the associated value of &lt;em&gt;a&lt;/em&gt;.&lt;/p&gt;&lt;p&gt;The analytical data confirmed that the ratio &amp;#964;&lt;sub&gt;crit&lt;/sub&gt;/&lt;em&gt;t&lt;/em&gt;&lt;sub&gt;max&lt;/sub&gt; was constant and equal to 1.495, regardless the combination of soil, ring diameter and initial water saturation. The calculated &lt;em&gt;a&lt;/em&gt; values varied between 0.706 and 0.904, with a mean equal to &lt;em&gt;a&lt;/em&gt; = 0.807, and were independent of the initial water content for saturation degrees up to approximately 0.50.&lt;/p&gt;&lt;p&gt;Application of the optimization procedure to field data was problematic given it was successful only in 29 out of 70 infiltration tests. Fixing &amp;#964;&lt;sub&gt;crit&lt;/sub&gt;&lt;em&gt;a-priori&lt;/em&gt; could be advisable in this case and it was shown that two alternative empirical criteria for selecting &amp;#964;&lt;sub&gt;crit&lt;/sub&gt; yielded &lt;em&gt;a&lt;/em&gt; values differing by a nearly negligible mean factor of 1.10 and significantly correlated to one another (&lt;em&gt;R&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; = 0.997).&lt;/p&gt;&lt;p&gt;However, a rather high percentage of &lt;em&gt;a&lt;/em&gt; values (45.5%) were greater than the theoretical maximum value (&lt;em&gt;a&lt;/em&gt; = 1), and therefore were physically implausible. Excluding these values from the analysis, the mean &lt;em&gt;a&lt;/em&gt; parameter (&lt;em&gt;a&lt;/em&gt; = 0.735) was close to that estimated by the successful applications of the optimization procedure (&lt;em&gt;a&lt;/em&gt; = 0.673).&lt;/p&gt;&lt;p&gt;Therefore, consistent results were obtained by field and analytical data with &lt;em&gt;a&lt;/em&gt; values intermediate between the suggested values in the literature (&lt;em&gt;a&lt;/em&gt; = 0.45 and 0.91). These findings can inform parameterization choices for others working with infiltration models, and should reduce uncertainty during interpretation of infiltration measurements.&lt;/p&gt;

Biting midge dynamics and bluetongue transmission: a multiscale model linking catch data with climate and disease outbreaks

Bluetongue virus (BTV) serotype 8 has been circulating in Europe since a major outbreak occurred in 2006, causing economic losses to livestock farms. The unpredictability of the biting activity of midges that transmit BTV implies difficulty in computing accurate transmission models. This study uniquely integrates field collections of midges at a range of European latitudes (in Sweden, The Netherlands, and Italy), with a multi-scale modelling approach. We inferred the environmental factors that influence the dynamics of midge catching, and then directly linked predicted midge catches to BTV transmission dynamics. Catch predictions were linked to the observed prevalence amongst sentinel cattle during the 2007 BTV outbreak in The Netherlands using a dynamic transmission model. We were able to directly infer a scaling parameter between daily midge catch predictions and the true biting rate per cow per day. Compared to biting rate per cow per day the scaling parameter was around 50% of 24 h midge catches with traps. Extending the estimated biting rate across Europe, for different seasons and years, indicated that whilst intensity of transmission is expected to vary widely from herd to herd, around 95% of naïve herds in western Europe have been at risk of sustained transmission over the last 15 years.

Diversity scaling of human digestive tract (DT) microbiomes: the intra-DT and inter-individual patterns

The human gut microbiome has been extensively studied, but its diversity scaling (changes) along the DT ( digestive tract ) as well as their inter-individual heterogeneities have not been adequately addressed in our opinion. Here we fill the gap by applying the diversity-area relationship (DAR), a recent extension to the classic species-area relationship (SAR) in biogeography, by reanalyzing the dataset of over 2000 16s-rRNA microbiome samples obtained from 10 DT sites of over 200 individuals. We sketched out the biogeography “maps” for each of the 10 DT sites by cross-individual DAR analysis, and the intra-DT distribution pattern by cross-DT site DAR analysis. Regarding the inter-individual biogeography, it was found that all DT sites have the invariant scaling parameter —all sites possessing the same diversity change rate across individuals, but most sites have different potential diversities. In terms of the genus richness, an average individual hosts approximately 20% of the population-level genus richness (total bacterial genus of a human population). In contrast, in terms of community biodiversity, the percentages of individual vs . population may exceed 90%. This suggests that the differences between individuals in their DT microbiomes are predominantly in the composition of bacterial species, rather than how their abundances are distributed ( i.e ., biodiversity). Regarding the intra-DT patterns, the scaling parameter is larger—suggesting that the intra-DT biodiversity changes are more dramatic than inter-individual changes. On average, each site contains 21%-36% of genus diversity of the whole DT, and the percentages are even higher at the higher taxon levels.