Extended law of corresponding states: square-well oblates

The vapour-liquid coexistence collapse in the reduced temperature, Tr=T/Tc, reduced density, ρr= ρ/ρc, plane is known as a principle of corresponding states, and Noro and Frenkel have extended it for pair potentials of variable range. Here, we provide a theoretical basis supporting this extension and show that it can also be applied to short-range pair potentials where both repulsive and attractive parts can be anisotropic. We observe that the binodals of oblate hard ellipsoids for a given aspect ratio (κ=1/3) with varying short-range square-well interactions collapse into a single master curve in the Δ B*2--ρr plane, where Δ B*2= (B2(T)-B*2(Tc))/v0, B2 is the second virial coefficient, and v0 is the volume of the hard body. This finding is confirmed by both REMC simulation and second virial perturbation theory for varying square-well shells, mimicking uniform, equator, and pole attractions. Our simulation results reveal that the extended law of corresponding states is not related to the local structure of the fluid.

Astral hydrogels mimic tissue mechanics by aster-aster interpenetration

Many soft tissues are compression-stiffening and extension-softening in response to axial strains, but common hydrogels are either inert (for ideal chains) or tissue-opposite (for semiflexible polymers). Herein, we report a class of astral hydrogels that are structurally distinct from tissues but mechanically tissue-like. Specifically, hierarchical self-assembly of amphiphilic gemini molecules produces radial asters with a common core and divergently growing, semiflexible ribbons; adjacent asters moderately interpenetrate each other via interlacement of their peripheral ribbons to form a gel network. Resembling tissues, the astral gels stiffen in compression and soften in extension with all the experimental data across different gel compositions collapsing onto a single master curve. We put forward a minimal model to reproduce the master curve quantitatively, underlying the determinant role of aster-aster interpenetration. Compression significantly expands the interpenetration region, during which the number of effective crosslinks is increased and the network strengthened, while extension does the opposite. Looking forward, we expect this unique mechanism of interpenetration to provide a fresh perspective for designing and constructing mechanically tissue-like materials.

Studies on the structure, optical, ac conduction mechanism by OLPT model and impedance spectroscopy of La-doped Ba2SnO4 Ruddlesden Popper Oxide

The conventional ceramic route has been used to prepare the La-doped Ba2SnO4 samples by heat-treatment at 1000oC and sintered at 1250oC. The phase identification was carried out using XRD and found to be single phase up to 4 atoms %. The solubility of La at Ba-site were further reconfirmed using FTIR and Raman analysis. The AC conductivity spectra of all samples follow universal Johnscher’s power law; however, the thermal dependence of suggest Arrhenius type conduction within the sample. Further, the scaled conductivity and frequency at all temperatures superimposes on a single master curve, indicates the invariance of conduction mechanism. The impedance spectroscopy studies suggest the major contribution of grain in the conduction and relaxation. The present material could be potentially used in semiconductor device, UV-detector, and mixed ionic and electronic conductor (MIECs) by utilizing absorption states and thermo-curves as metastable state.

Mesoscale Anisotropy in Porous Media Made of Clay Minerals. A Numerical Study Constrained by Experimental Data

The anisotropic properties of clay-rich porous media have significant impact on the directional dependence of fluids migration in environmental and engineering sciences. This anisotropy, linked to the preferential orientation of flat anisometric clay minerals particles, is studied here on the basis of the simulation of three-dimensional packings of non-interacting disks, using a sequential deposition algorithm under a gravitational field. Simulations show that the obtained porosities fall onto a single master curve when plotted against the anisotropy value. This finding is consistent with results from sedimentation experiments using polytetrafluoroethylene (PTFE) disks and subsequent extraction of particle anisotropy through X-ray microtomography. Further geometrical analyses of computed porous media highlight that both particle orientation and particle aggregation are responsible of the evolution of porosity as a function of anisotropy. Moreover, morphological analysis of the porous media using chord length measurements shows that the anisotropy of the pore and solid networks can be correlated with particle orientation. These results indicate that computed porous media, mimicking the organization of clay minerals, can be used to shed light on the anisotropic properties of fluid transfer in clay-based materials.

Tuning transcriptional regulation through signaling: A predictive theory of allosteric induction

Allosteric regulation is found across all domains of life, yet we still lack simple, predictive theories that directly link the experimentally tunable parameters of a system to its input-output response. To that end, we present a general theory of allosteric transcriptional regulation using the Monod-Wyman-Changeux model. We rigorously test this model using the ubiquitous simple repression motif in bacteria by first predicting the behavior of strains that span a large range of repressor copy numbers and DNA binding strengths and then constructing and measuring their response. Our model not only accurately captures the induction profiles of these strains but also enables us to derive analytic expressions for key properties such as the dynamic range and [EC50]. Finally, we derive an expression for the free energy of allosteric repressors which enables us to collapse our experimental data onto a single master curve that captures the diverse phenomenology of the induction profiles.

Viscoelastic flow past mono- and bidisperse random arrays of cylinders: flow resistance, topology and normal stress distribution

Different flow resistance curves for viscoelastic flows through random arrangements of cylinders collapse to a single master curve when plotted against a Deborah number based on the square root of the permeability as characteristic length scale.

Inertial rise of a meniscus on a vertical cylinder

We consider the inertia-dominated rise of a meniscus around a vertical circular cylinder. Previous experiments and scaling analysis suggest that the height of the meniscus, $h_{m}$, grows with the time following the initiation of rise, $t$, like $h_{m}\propto t^{1/2}$. This is in contrast to the rise on a vertical plate, which obeys the classic capillary–inertia scaling $h_{m}\propto t^{2/3}$. We highlight a subtlety in the scaling analysis that yielded $h_{m}\propto t^{1/2}$ and investigate the consequences of this subtlety. We develop a potential flow model of the dynamic problem, which we solve using the finite element method. Our numerical results agree well with previous experiments but suggest that the correct early time behaviour is, in fact, $h_{m}\propto t^{2/3}$. Furthermore, we show that at intermediate times the dynamic rise of the meniscus is governed by two parameters: the contact angle and the cylinder radius measured relative to the capillary length scale, $t^{2/3}$. This result allows us to collapse previous experimental results with different cylinder radii (but similar static contact angles) onto a single master curve.

Rupture Process During Drop Coalescence

During the coalescence of a drop with a planar interface, a hole is generated in a microscopic film that separates the drop from the interface. An experimental study has been performed to investigate the time dependent behavior of the radius of the hole generated during coalescence. The study consisted of placing drops of various sizes and physical properties on a planar interface. The coalescence process was recorded from underneath the interface with the aid of a high speed digital camera and a prism. The experiment captured two separate processes, film rupture and the closing of the hole. During the film rupture, the hole radius demonstrated a power law time dependence. Dimensional analysis showed the percentage of time the hole used to reach its maximum radius was approximately constant for all drops. Moreover, all dimensionless drop rupture radii and times fit onto a single master curve and were independent of their physical properties during the opening. However during the closing of the hole, the dimensionless time and radii did not fit a master curve analogous to the hole rupture. The closing of the hole is an entirely different event from the opening and is governed by different parameters.

A General Correlation for the Hydraulic Permeability of Arrays of Elliptical Fiber Bundles

A computational analysis of viscous flow through arrays of fiber bundles is carried out using the Boundary Element Method. We consider fiber bundles of elliptical cross section, each made up of up to 350 individual filaments. Such arrays are dual-porosity systems, characterized by different inter- (ϕi) and intra-tow (ϕt) porosities as well as by varying number (Nf) of filaments within each bundle. Investigating the influence of these parameters on the hydraulic permeability of hexagonal arrays of such bundles is the subject of our simulations. The results are compared to earlier analytical models and a good agreement is found. A dimensionless correlation is proposed and the computed permeabilities for bundles of aspect ratio λ = 2 and λ = 3 are shown to fall on a single master curve. This offers a generalized model for the calculation of the permeability of such dual porosity systems from knowledge of ϕi, ϕt, λ and Nf.