The European Physical Journal E最新文献

Root hairs are outgrowths of the epidermal cells of plant roots. They increase the root's exchange surface with the soil and provide it with good anchorage in the soil. Root hairs are an emblematic model of apical growth, a process also used by yeasts and hyphae to invade their environment. From a mechanical perspective, the root hair is considered as an elastic cylinder under pressure, closed by a dome that behaves like a yield fluid. We introduce here two innovative mechanical setups and protocols to characterize the mechanical properties of single growing root hairs in Arabidopsis thaliana. In the first setup, root hairs grow against an elastic obstacle until buckling. By measuring the critical buckling force, we determine the surface modulus and estimate the Young's modulus of the cell wall, which aligns with previous measurements. Using a 1D elasto-viscoplastic model of root hair growth, we assess the excess pressure beyond the yield threshold (the driver of tip growth) and estimate the axial stiffness of the root hair, reflecting its elastic resistance to compression. For the second protocol, we designed a setup where a single root hair grows against a cantilever with variable stiffness, a technique adapted from our earlier work on rigidity sensing by animal cells. This method provides an independent estimate of the root hair's axial stiffness, confirming our initial findings and suggesting that this stiffness primarily involves tip compression and depends mainly on turgor pressure, at least within the low deformation regime explored.

This work investigates the linear stability of a thin liquid film flowing down a uniformly heated vertical cylindrical fiber. A fourth-order nonlinear evolution equation governing the spatiotemporal dynamics of the film thickness is derived using lubrication approximation and asymptotic expansion. The model captures the influence of gravity, inertia, surface tension, thermocapillarity, and convective heat transfer through key dimensionless parameters: Bond, Reynolds, Marangoni, and Biot numbers. Temporal stability analysis reveals that, in the absence of inertia and thermocapillarity, perturbations grow due to the classical Rayleigh-Plateau instability. Moderate inertia enhances instability, although Rayleigh-Plateau instability remain dominant over inertial instability for high surface tension fluids. The relative influence of gravity and surface tension, represented by the Bond number, tends to stabilize long-wave disturbances ( $k<1$ ) while promoting the growth of short-wave modes ( $k>1$ ). Thermocapillary stress stabilizes film flow on a cooled cylinder and destabilizes it on a heated one. The Biot number plays a dual role-initially amplifying instability, then reducing it as interfacial temperature gradients diminish. Spatiotemporal analysis uncovers a transition from convective to absolute instability with increasing Marangoni or Reynolds numbers. Lower Bond numbers favor absolute instability, which transitions to convective behavior as Bond number increases. Numerical simulations align well with theoretical predictions, capturing both temporal and spatiotemporal film dynamics under varying physical conditions.

Dielectric spectroscopy measurements of bulk and emulsified high-density amorphous ices (HDA) at 1.0 GPa were carried out to examine the effect of emulsion matrix on the dielectric spectra. The presence of emulsion matrix induces the shifts of the loss peak to higher frequency side. The degree of shift depends on the volume fraction of the emulsion matrix to HDA. This indicates that the relaxation time obtained from the dielectric spectra of emulsified HDA is underestimated than the true relaxation time of HDA. The results suggest that the emulsified sample is not appropriate for dielectric spectroscopy measurement in water polyamorphism study, although the emulsification is effective, for example, in avoiding water crystallization.

Chemical graph theory provides a mathematical framework for representing molecular structures as graphs, where atoms correspond to vertices and chemical bonds to edges. This approach enables the use of molecular descriptors to extract reliable structural information and model physicochemical properties. In this study, we investigate the use of recently introduced degree-based molecular descriptors including Euler Sombor, elliptic Sombor, reverse Sombor, reverse elliptic Sombor, reverse Euler Sombor, Lanzhou, and ad-hoc Lanzhou indices to model key properties of polychlorinated biphenyls (PCBs). Experimentally reported properties such as melting point, relative retention time, octanol-water partition coefficient, enthalpy of formation, and Henry’s law constant were analyzed. Quantitative structure–property relationship models were developed using linear, polynomial, and ridge regression techniques. The predictive performance of these models was evaluated through comparison of actual and predicted values, cross-validation, and bootstrapping. Results indicate that the selected descriptors, particularly the elliptic Sombor and reverse Euler Sombor indices, exhibit strong correlations with PCB properties, demonstrating their utility in predicting physicochemical behavior. These models hold potential for applications in chemical ecology, environmental risk assessment, and computational molecular design.

We examine the reaction of a homogeneous spherical fluid vesicle to the force exerted by a rigid circular ring located at its equator in the linear regime. We solve analytically the linearized first integral of the Euler–Lagrange equation subject to the global constraints of fixed area and volume, as well as to the local constraint imposed by the ring. We determine the first-order perturbations to the generating curve of the spherical membrane, which are characterized by the difference of the radii of the membrane and the ring, and by a parameter depending on the physical quantities of the membrane. We determine the total force that is required to begin the deformation of the membrane, which gives rise to a discontinuity in the curvature of the membrane across the ring.

We study water uptake in plants by modelling the xylem as a narrow capillary tube through which sap rises under transpiration pull. We modify the classical Bosanquet equation, incorporating the effect of friction f, arising from xylem wall protrusions, while including corrections to the surface tension due to the presence of ions in the sap and due to local curvature via the Tolman correction. We also take into consideration an externally imposed transpiration flux. We identify a dimensionless tuning parameter, (xi ), that is a relative measure of capillary to hydrostatic forces that, along with f, affects system behaviour. In the absence of transpiration, transitions between oscillatory and non-oscillatory behavior of the sap column depends on (xi ), while its rate of rise depends on f. We find that the addition of transpiration to the xylem capillary system, by considering diffusion and evaporation at the leaves, causes the system to instead stabilize around a nonlinear center, also crucially increasing the maximal height to which the water rises. We obtain scaling power-laws for the time required for the sap to reach to reach its maximum height, and the characteristic time scale for oscillations in the column to decay to its fixed point, as functions, respectively, of f and of (xi ). We investigate the competitive effects of transpiration pull and presence of corrugation in the conduits. Our approach integrates capillary flow physics with dynamical systems theory to uncover new insights and get a more comprehensive and novel understanding of the problem of water transport in plants.

Modelling sap rise in xylem as flow through a corrugated capillary, including the effects of charged ions and corrugation friction, as well as transpiration from the leaves.

We present a practical white-light interferometric method, supported by an open-source Python library optifik for automated spectrum-to-thickness deduction, enabling foam film measurements down to a few nanometers. We describe three typical spectral scenarii encountered in this method: spectra exhibiting numerous interference fringes, spectra with a moderate number of peaks, and spectra with only a few identifiable features, providing illustrative examples for each case. We also discuss the main limitations of the technique, including spectral range constraints, the necessity of knowing the refractive index, and the influence of spectral resolution and signal quality. Finally, we demonstrate the application of the method in a time-resolved study of a TTAB (tetradecyltrimethylammonium bromide) foam film undergoing elongation and thinning. This method can be adapted to measure any thin non-opaque layer.

This work investigates chiral particles, which break mirror symmetry, in turbulent Taylor–Couette flow. These particles generally display a translation-rotation coupling moving through a quiescent fluid. Here, we performed experiments using large chiral particles (typical size 5mm) in turbulent Taylor–Couette flow, for Reynolds numbers (9cdot 10^3 le text {Re} le 1.5 cdot 10^5). The density-matched chiral particles are studied in a dilute regime ((phi = 1.7 cdot 10^{-4})), where their location and orientation are tracked over time to investigate the particle-fluid coupling. We investigate whether the translation-rotation coupling observed at low Reynolds numbers is still observable over the measured high Reynolds numbers, using the tracked location and orientation. Similarly, we verify whether the chiral particles display a preferred location or orientation, and whether the left-handed and right-handed particles show different rotation statistics. The location data show that the chiral particles closely follow the structure of Taylor vortices. Hence, the orientation data and rotation data of the chiral particles are split between the Taylor vortices and particle chiralities. The results show no difference in rotation and orientation dynamics between chiralities. Rather, the particle dynamics are flow-dominated, where the flow vorticity determines the specific particle dynamics.

An illustration of chiral particles and the Taylor-Couette setup used in this research (left panel). The typical length scale for the particles is (l = 3.5) mm, whereas the gap width between the cylinders of the Taylor-Couette is (d = 30) mm. The particle trajectories and a vector plot of the radial and axial velocity components in a radial slice (right panel). Black lines are added to illustrate the boundaries the vortices.