2063 research outputs found
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Aggregation and disaggregation of red blood cells: Depletion versus bridging
Full text linkThe aggregation of red blood cells (RBCs) is a complex phenomenon that strongly impacts blood flow and tissue perfusion. Despite extensive research for more than 50 years, physical mechanisms that govern RBC aggregation are still under debate. Two proposed mechanisms are based on bridging and depletion interactions between RBCs due to the presence of macromolecules in blood plasma. The bridging hypothesis assumes the formation of bonds between RBCs through adsorbing macromolecules, while the depletion mechanism results from the exclusion of macromolecules from the intercellular space, leading to effective attraction. Existing experimental studies generally cannot differentiate between these two aggregation mechanisms, although several recent investigations suggest concurrent involvement of the both mechanisms. We explore dynamic aggregation and disaggregation of two RBCs using three simulation models: a potential-based model mimicking depletion interactions, a bridging model with immobile bonds, and a new bridging model with mobile bonds that can slide along RBC membranes. Simulation results indicate that dynamic aggregation of RBCs primarily arises from depletion interactions, while disaggregation of RBCs involves both mechanisms. The bridging model with mobile bonds reproduces well the corresponding experimental data, offering insights into the interplay between bridging and depletion interactions and providing a framework for studying similar interactions between other biological cells
A SEMI-ANALYTICAL SOLUTION FOR THE LUBRICATION FORCE BETWEEN TWO SPHERES APPROACHING IN VISCOELASTIC FLUIDS DESCRIBED BY THE OLDROYD-B MODEL UNDER SMALL DEBORAH NUMBERS
Full text linkViscoelastic fluids play a critical role in various engineering and biological applications, where their
lubrication properties are strongly influenced by relaxation times ranging from microseconds to min-
utes. Although the lubrication mechanism for Newtonian fluids is well-established, its extension into
viscoelastic materials—particularly under squeezing flow conditions—remains less explored. This
study presents a semi-analytical solution for the lubrication force between two spheres approaching
in a Boger fluid under small Deborah numbers. Unlike previous works that assumed a Newtonian
velocity field, we derive the velocity profile directly from the mass-momentum conservation and
Oldroyd-B constitutive equations using lubrication theory and order-of-magnitude analysis techniques.
Under steady-state conditions, viscoelasticity induces a marginal increase in the surface-to-surface
normal force as a result of the increased pressure required to overcome the resistance originating
from the first normal-stress difference. Transient analyses reveal that the normal lubrication force is
bounded by two Newtonian plateaus and is non-symmetric as the spheres approach or separate. Our
findings highlight the role of viscoelasticity in improving load capacity and provide new insights for
modelling dense particle suspensions in Boger fluids, where short-range interactions dominate
Non-Linear Operator-valued Elliptic Flows with Application to Quantum Field Theory
Full text linkDifferential equations on spaces of operators are very little developed in Mathematics, being in general very challenging. Here, we study a novel system of such (non-linear) differential equations. We show it has a unique solution for all times, for instance in the Schatten norm topology. This system presents remarkable ellipticity properties that turn out to be crucial for the study of the infinite-time limit of its solution, which is proven under relatively weak, albeit probably not necessary, hypotheses on the initial data. This system of differential equations is the elliptic counterpart of an hyperbolic flow applied to quantum field theory to diagonalize Hamiltonians that are quadratic in the bosonic field. In a similar way, this elliptic flow, in particular its asymptotics, has application in quantum field theory: it can be used to diagonalize Hamiltonians that are quadratic in the fermionic field while giving new explicit expressions and properties of these pivotal Hamiltonians of quantum field theory and quantum statistical mechanics.Government through the grant IT1615-22 and the BERC 2022-2025 program, by
the grant PID2020-112948GB-I00 funded by MCIN/AEI/10.13039/501100011033 and
by ERDF A way of making Europe
Tracking interfaces in a random logistic free-boundary diffusion problems: a random level set method
No full textFree-boundary diffusive logistic model finds applications in diverse fields associated with
population dynamics. These processes often possess stochastic characteristics and involve
parameters with uncertainties. This study focuses on enhancing a two-dimensional diffusive
logistic partial differential model with free boundary by incorporating randomness in the
mean square sense, considering the conditions for well-posedness in the random case, which
is crucial for the further analysis. Both unknown stochastic processes the solution and its
moving front, and the parameters involved in the random problem as random variables, are
constrained by a finite degree of randomness. To tackle this challenge, we propose a random
level set method. Given the complexity of the problem, we employ alternating direction
explicit methods for the interior solvers, to effectively address computational challenges.
Since computing the mean and the standard deviation of both unknown stochastic processes
are required, we combine the sample approach of the difference schemes together with Monte
Carlo technique avoiding the storage accumulation of symbolic expressions of all the previ-
ous levels of the iteration process. Parallel computing is employed to enhance performance.
A careful numerical analysis is performed in the mean square context to ensure stability,
positivity, and boundedness. The set of presented examples illustrates these qualitative prop-
erties, assess numerical convergence and enables us to gain a deeper understanding of the
system’s behavior attending to the geometry of the initial habitat. This approach provides
valuable tools for analyzing and predicting spreading-vanishing dichotomy
Hilbert--Kunz multiplicity of quadrics via Ehrhart theory
No full textWe show that the Hilbert--Kunz multiplicity of the -dimensional non-degenerate quadric hypersurface of characteristic is a rational function of composed from the Ehrhart polynomials of integer polytopes.
In consequence, we recover a result of Trivedi on monotonicity of for , we recover and explain the Gessel--Monsky formula for the limit , and prove that is a decreasing function of for fixed.RYC2020-028976-
On low regularity well-posedness of the binormal flow
No full textAbstract. We focus on a class of solutions of the binormal flow, model of the evolution
of vortex filaments, that generate several corner singularities in finite time. This phenom-
enon has been studied in [4, 1] in the regular case, which in this context is in terms of the
summability of the angles of the corners generated. Our goal here is to investigate the
lower regularity case, using further the Hasimoto approach that allows to use the 1D cubic
nonlinear Schr¨odinger to study the binormal flow. We first obtain a deterministic result
by proving an existence result for general binormal flow solutions at low regularity. Then
we obtain improved results on the above class of solutions by a suitable randomization of
the curvature and torsion of the vortex filament. To do so, we prove a scattering result
for a quasi-invariance measure associated with a suitable 1D cubic nonlinear Schr¨odinger
equation that we consider of independent interest. An interesting feature of this result is
that we are able to identify a limit measure, which is usually not possible when working
on quasi-invariant Gaussian measures for Hamiltonian PDE’s on bounded domains
Degenerate Poincaré-Sobolev inequalities via fractional integration
No full textWe present a local weighted estimate for the Riesz potential in , which improves the main theorem of Alberico, Cianchi, and Sbordone [C. R. Math. Acad. Sci. Paris \textbf{347} (2009)] in several ways. As a consequence, we derive weighted Poincaré-Sobolev inequalities with sharp dependence on the constants. We answer positively to a conjecture proposed by Pérez and Rela [Trans. Amer. Math. Soc. \textbf{372} (2019)] related to the sharp exponent in the constant in the Poincaré-Sobolev inequality with weights. Our approach is versatile enough to prove Poincaré-Sobolev inequalities for high-order derivatives and fractional Poincaré-Sobolev inequalities with the BBM extra gain factor . In particular, we improve one of the main results from Hurri-Syrjänen, Martínez-Perales, Pérez, and Vähäkangas [Int. Math. Res. Not. \textbf{20} (2023)].PRE2021-09909
Analysis of the impact of fear in the presence of additional food and prey refuge with nonlocal predator-prey models
Full text linkThere are many positive and negative factors present in the predator-prey interaction which
affect the net growth of the species. Fear of predation is one such factor that creates psychological stress in a prey species, which causes a negative impact on their overall growth. This work
considers a predator-prey model where the prey species faces a reduction in their growth out of
fear, and the predator has an alternative food source that helps the prey to hide in a safer place.
As an extension into the nonlocal spatio-temporal model, a nonlocal term is considered in the
prey growth to incorporate a fear-effect range around their spatial location. Linear stability
analysis helps to analyze the temporal model and produces a wide range of interesting results,
including the presence of a certain amount of fear or even prey refuge, which helps in population
coexistence. Furthermore, the numerical simulations of the local and nonlocal spatio-temporal
models show different types of spatial-temporal patterns, such as Turing and non-Turing patterns. Nevertheless, an increase in fear level reduces the range of the Turing domain for the
local model, whereas the opposite happens when the range of nonlocal interaction is increased
A Transition State Resonance Radically Reshapes Angular Distributions of the F + H2 -> F H (vf = 3) + H Reaction in the 62.09-101.67 meV Energy Range
No full textReactive angular distributions of the benchmark F + H2(vi = 0) → FH(vf = 3) + H reaction show unusual propensity toward small scattering angles, a subject of a long debate in the literature. We use Regge trajectories to quantify the resonance contributions to state-to-state differential cross sections. Conversion to complex energy poles allows us to attribute the effect almost exclusively to a transition state resonance, long known to exist in the F + H2 system and its isotopic variant F + HD. For our detailed analysis of angular scattering we employ the package DCS_Regge, recently developed for the purpose [Akhmatskaya, E.; Sokolovski, D. Comput. Phys. Commun. 2022, 277, 108370].MICIU/AEI/10.13039/501100011033 and “ERDF A way for Europe”through BCAM Severo Ochoa accreditation CEX2021-001142-S/MICIU/AEI/10.13039/501100011033; PLAN COMPLE-MENTARIO MATERIALES AVANZADOS 2022-2025,PROYECTO No:1101288, and grant PID2022-136585NB-C22; as well as ELKARTEK program (the Basque Government) under Grants KK-2023/00017, KK-2024/00062 and the BERC 2022-2025 program (the Basque Government)