Turbulent parameters in the middle atmosphere: Theoretical estimates deduced from a gravity-wave resolving general circulation model

We present a scaling analysis for the stratified turbulent and small-scale turbulent regimes of atmospheric flow with emphasis on the mesosphere. We distinguish rotating-stratified macroturbulence turbulence (SMT), stratified turbulence (ST), and small-scale isotropic Kolmogorov turbulence (KT), and we specify the length and time scales and the characteristic velocities for these regimes. It is shown that the buoyancy scale (Lb) and the Ozmidov scale (Lo) are the main parameters that describe the transition from SMT to KT. We employ the buoyancy Reynolds number and horizontal Froude number to characterize ST and KT in the mesosphere. This theory is applied to simulation results from a high-resolution general circulation model with a Smagorinsky-type turbulent diffusion scheme for the sub-grid scale parameterization. The model allows us to derive the turbulent root-mean-square (RMS) velocity in the KT regime. It is found that the turbulent RMS velocity has a single maximum in summer and a double maximum in winter months. The secondary maximum in the winter MLT we associate with a secondary gravity wave breaking phenomenon. The turbulent RMS velocity results from the model agree well with Full Correlation Analyses based on MF-radar measurements. A new scaling for the mesoscale horizontal velocity based on the idea of direct energy cascade in masoscales is proposed. The latter findings for mesoscale and small-scale characteristic velocities supports the idea proposed in this research that mesoscale and small-scale dynamics in the mesosphere are governed by SMT, ST, and KT in the statistical average.

Exploring arterial tissue microstructural organization using non-Gaussian diffusion magnetic resonance schemes

The purpose of this study was to characterize the alterations in microstructural organization of arterial tissue using higher-order diffusion magnetic resonance schemes. Three porcine carotid artery models namely; native, collagenase treated and decellularized, were used to estimate the contribution of collagen and smooth muscle cells (SMC) on diffusion signal attenuation using gaussian and non-gaussian schemes. The samples were imaged in a 7 T preclinical scanner. High spatial and angular resolution diffusion weighted images (DWIs) were acquired using two multi-shell (max b-value = 3000 s/mm2) acquisition protocols. The processed DWIs were fitted using monoexponential, stretched-exponential, kurtosis and bi-exponential schemes. Directionally variant and invariant microstructural parametric maps of the three artery models were obtained from the diffusion schemes. The parametric maps were used to assess the sensitivity of each diffusion scheme to collagen and SMC composition in arterial microstructural environment. The inter-model comparison showed significant differences across the considered models. The bi-exponential scheme based slow diffusion compartment (Ds) was highest in the absence of collagen, compared to native and decellularized microenvironments. In intra-model comparison, kurtosis along the radial direction was the highest. Overall, the results of this study demonstrate the efficacy of higher order dMRI schemes in mapping constituent specific alterations in arterial microstructure.

Computational modeling predicts acidic microdomains in the glutamatergic synaptic cleft

At chemical synapses, synaptic vesicles release their acidic contents into the cleft leading to the expectation that the cleft should acidify. However, fluorescent pH probes targeted to the cleft of conventional glutamatergic synapses in both fruit flies and mice reveal cleft alkalinization, rather than acidification. Here, using a reaction-diffusion scheme, we modeled pH dynamics at the Drosophila neuromuscular junction (NMJ) as glutamate, adenosine triphosphate (ATP) and protons (H+) are released into the cleft. The model incorporates bicarbonate and phosphate buffering systems as well as plasma membrane calcium-ATPase (PMCA) activity and predicts substantial cleft acidification but only for fractions of a millisecond following neurotransmitter release. Thereafter, the cleft rapidly alkalinizes and remains alkaline for over 100 milliseconds, as the PMCA removes H+ from the cleft in exchange for calcium ions (Ca2+) from adjacent pre- and post-synaptic compartments; thus recapitulating the empirical data. The extent of synaptic vesicle loading and time course of exocytosis has little influence on the magnitude of acidification. Phosphate, but not bicarbonate buffering is effective at ameliorating the magnitude and time course of the acid spike, while both buffering systems are effective at ameliorating cleft alkalinization. The small volume of the cleft levies a powerful influence on the magnitude of alkalinization and its time course. Structural features that open the cleft to adjacent spaces appear to be essential for alleviating the extent of pH disturbances accompanying neurotransmission.

Influence of survival, promotion, and growth on pattern formation in zebrafish skin

The coloring of zebrafish skin is often used as a model system to study biological pattern formation. However, the small number and lack of movement of chromatophores defies traditional Turing-type pattern generating mechanisms. Recent models invoke discrete short-range competition and long-range promotion between different pigment cells as an alternative to a reaction-diffusion scheme. In this work, we propose a lattice-based “Survival model,” which is inspired by recent experimental findings on the nature of long-range chromatophore interactions. The Survival model produces stationary patterns with diffuse stripes and undergoes a Turing instability. We also examine the effect that domain growth, ubiquitous in biological systems, has on the patterns in both the Survival model and an earlier “Promotion” model. In both cases, domain growth alone is capable of orienting Turing patterns above a threshold wavelength and can reorient the stripes in ablated cells, though the wavelength for which the patterns orient is much larger for the Survival model. While the Survival model is a simplified representation of the multifaceted interactions between pigment cells, it reveals complex organizational behavior and may help to guide future studies.

Facile Synthesis of CeO2 Blended CoWO4 Nanocomposites For High Photocatalytic Performance And Investigation of Their Antimicrobial Activity

In this work, novel CeO2/CoWO4 hetero structured nanocomposites (NCs) was synthesized via a hydrothermal method. X-ray diffraction (XRD), high-resolution transmission electron microscopy(HRTEM), UV-VisDRS and photo luminescence (PL) spectroscopy were categorized herein to gain the crystal structure, deep morphology, optical assets, and charge separation of the as-produced photocatalysts (PCs)respectively. Related by the pristine CoWO4,CeO2 and CeO2/CoWO4 photocatalyst was considered by enriched activity of them ethylene blue (MB)aqueous dye photodegradation under visible light exposure. Chiefly, the photodegradation efficacy of as-attained CeO2/CoWO4 photocatalyst exposed the premier decomposition ratio (92.5%) of MB dyein105 min among all samples, which was noticeably 1.8 and 2.2 folds over the pristine CeO2 (43 %) and CoWO4(60 %), separately. Likewise, the CeO2/CoWO4 PCs sustained satisfactory activity even after 4sequentialrecycling runs, signifying its great photocatalytic steadiness and robustness. Hence the ensuing superior PCs preferred the further efficient charge (e−-h+) separation, solid visible light fascination, and worthy interfacial energy transfer leads amid CoWO4 and CeO2nanoparticles (NPs).A likely mechanism liable for photodegradation was eventually projected. The synergistic things of antibacterial motion via CeO2/CoWO4 NCs were probed by the weld diffusion scheme. Thus, effort finding deals with a novel avenue for the growth of stable and proficient visible-light active PCs for environmental purification.

Assessing a planetary boundary layer scheme by using the GABLS1 experiment in a single-column version of the global model developed based on potential vorticity

<p>Determining the accuracy of a hydrostatic weather forecast model in representing atmospheric phenomena is a complex process involving various considerations and test cases. This study delineates an objective assessment of a planetary boundary layer scheme based on turbulent kinetic energy in a single-column version of the innovative atmospheric general circulation model developed at the University of Tehran, which is called UTGAM. Single-column models provide simple frameworks to investigate the fidelity of the simulated physical processes in the atmospheric models. Dependable parameterization of the boundary layer processes has significant impacts on weather forecasts. Specifically, an ongoing issue for the operational hydrostatic models is their deficiencies in the accurate representation of the unresolved processes in stably stratified conditions.</p><p>We have utilized the first GABLS intercomparison experiment set up as a simple tool to evaluate the diffusion scheme in the UTGAM. Two different sigma-theta and sigma-pressure single-column grid staggering combined with 33 and 14 vertical levels below 3 km height have been used for the low- and high-resolution simulations. The GABLS1 Large Eddy Simulation (LES) results have been used as a benchmark for comparison. The diffusion scheme explored here is the same as the one in the ECHAM model which has been adapted for use in the UTGAM.</p><p>Results depict subtle nuances between the sigma-theta and sigma-pressure coordinates in intercomparison between the low and high vertical resolutions separately, which are more apparent in the lower vertical resolution. Nevertheless, it seems that the diffusion processes have been simulated a bit more accurately in the high-resolution sigma-pressure vertical coordinate. The boundary layer scheme in the UTGAM analogous with most of the operational models in the GABLS1 intercomparison experiment overestimate the diffusion coefficients of momentum and heat. The wind profile with height depicts maxima that are higher than the corresponding LES profile. It is inferred that the scheme mixed momentum over a deeper layer than the LES, but the simulated wind profile is better compared to the other operational models in GABLS1. Considering the vertical profiles of potential temperature revealed that the amount of heat mixing is not suitable in this experiment and causes a negative bias in the lower part of the simulated boundary layer. The simulated amounts of surface friction velocity have proved significant differences with the LES results in all separate experiments. However, the latter large amounts seem unlikely to have a detrimental effect on forecast scores in the operational model. Moreover, the sensitivity of the scheme to the lowest full-level has been partially explored. Decreasing the lowest full-level height concurrent with increasing the vertical resolution exerts a modest influence on the simulation of the boundary layer processes. All the results confirm notable improvements by increasing the vertical resolution in both sigma-theta and sigma-pressure coordinates.</p><p><strong>Keywords:</strong> Simulation, GABLS1, stable boundary layer, vertical coordinate, diffusion coefficients, UTGAM</p>

Size matters: An analytical study on the role of tissue size in spatiotemporal distribution of morphogens unveils a transition between different Reaction-Diffusion regimes

The reaction-diffusion model constitutes one of the most influential mathematical models to study the distribution of morphogens spreading within tissues. Despite its widespread appearance, the role that the finitude of the tissue plays in the spatiotemporal morphogen distribution predicted by the model has not been unveiled so far. In this study, we investigated the spatiotemporal distribution of a morphogen predicted by a reaction-diffusion model in a 1D finite domain as a proxy to simulate a biological tissue. We analytically solved, for the first time to our knowledge, the model assuming morphogen produced de novo within a finite domain and compared it with the scenario considering an infinite domain, which was previously solved. We explored the only relevant parameter in the reduced model, the tissue length in units of a characteristic reaction-diffusion length, and fully characterized the model behavior in terms of: i) geometrical aspects of the spatial distributions and ii) kinetic features derived from the time elapsed to reach the steady state. We found a critical tissue size that we estimated as ∼3.3 characteristic reaction-diffusion lengths, above which the model assuming the infinite domain could suffice as a reasonable approximation. In contrast, for tissues smaller than the critical size, the error of assuming an infinite domain could rapidly accumulate, indicating that the model assuming finite domains is a better description. This new solution could replace the one used to estimate diffusion coefficients and degradation constants during the analysis of Fluorescence Recovery After Photobleaching (FRAP) experiments and it could also help to improve the performance of multiscale computational approaches, which involve a morphogen dynamics scale, typically modeled with a reaction diffusion scheme. These findings could drive new modeling strategies to understand tissue morphogenesis as well as cancer invasion, among many other relevant problems in biology and medicine.

Effect of Coulomb diffusion of ions on the pulsational properties of DA white dwarfs

Context. Element diffusion is a key physical process that substantially affects the superficial abundances, internal structure, pulsation properties, and evolution of white dwarfs. Aims. We study the effect of Coulomb separation of ions on the cooling times of evolving white dwarfs, their chemical profiles, the Brunt–Väisälä (buoyancy) frequency, and the pulsational periods at the ZZ Ceti instability strip. Methods. We followed the full evolution of white dwarf models in the range 0.5 − 1.3 M⊙ derived from their progenitor history on the basis of a time-dependent element diffusion scheme that incorporates the effect of gravitational settling of ions due to Coulomb interactions at high densities. We compared the results for the evolution and pulsation periods of ZZ Ceti stars with the case where this effect is neglected. Results. We find that Coulomb sedimentation profoundly alters the chemical profiles of ultra-massive (M⋆ ≳ 1 M⊙) white dwarfs throughout their evolution, preventing helium from diffusing inward toward the core, and thus leading to much narrower chemical transition zones. As a result, significant changes in the g-mode pulsation periods as high as 15% are expected for ultra-massive ZZ Ceti stars. For lower mass white dwarfs, the effect of Coulomb separation is much less noticeable. It causes period changes in ZZ Ceti stars that are below the period changes that result from uncertainties in progenitor evolution, but larger than the typical uncertainties of the observed periods. Conclusions. Coulomb diffusion of ions profoundly affects the diffusion flux in ultra-massive white dwarfs, driving the gravitational settling of ions with the same A/Z (mass to charge number). We show that it strongly alters the period spectrum of such white dwarfs, which should be taken into account in detailed asteroseismological analyses of ultra-massive ZZ Ceti stars.

Asteroseismology of the DAV star R808

ABSTRACT The DAV star R808 was observed by 13 different telescopes for more than 170 h in 2009 April on the WET run XCOV26. 25 independent pulsation frequencies were identified by this data set. We assumed 19 m = 0 modes and performed an asteroseismological study on those 19 modes. We evolve grids of DAV star models by wdec adopting the element diffusion scheme with pure and screened Coulomb potential effect. The core compositions are from white dwarf models evolved by mesa, which are thermal nuclear burning results. Our best-fitting model is from the screened Coulomb potential scenario, which has parameters of log(MHe/M*) = −2.4, log(MH/M*) = −5.2, Teff = 11100 K, M* = 0.710 M⊙, logg = 8.194, and σRMS = 2.86 s. The value of σRMS is the smallest among the four existing asteroseismological work. The average period spacing is 46.299 s for l = 1 modes and 25.647 s for l = 2 modes. The other six observed modes can be fitted by $m\, \ne$ 0 components of some modes for our best-fitting model. Fitting the 25 observed modes, we obtain a σRMS value of 2.59 s. Considering the period spacings, we also assume, that at least in one case, we detect an l = 2 trapped mode.