Single-particle and collective slow dynamics of colloids in porous confinement

Using molecular dynamics simulations we study the slow dynamics of a hard sphere fluid confined in a disordered porous matrix. The presence of both discontinuous and continuous glass transitions as well as the complex interplay between single-particle and collective dynamics are well captured by a recent extension of mode-coupling theory for fluids in porous media. The degree of universality of the mode-coupling theory predictions for related models of colloids is studied by introducing size-disparity between fluid and matrix particles, as well as softness in the interactions.Comment: 4 pages, 5 figures, minor revision

Recent breeding records of storks in Eastern Africa

Volume: XXVI

REVENUE INSURANCE FOR GEORGIA AND SOUTH CAROLINA PEACHES

We estimate actuarially fair premium rates for yield and revenue insurance for Georgia and South Carolina peaches. The premium rates for both products decrease at a decreasing rate as the mean farm-level yield increases. In general, the premium rate for revenue insurance exceeds the premium rate for yield insurance for a given coverage level and expected yield. Although the revenue and yield insurance rates differ in a statistical sense, they do not appear to differ in an economic sense except at high coverage levels for growers with very high yields.crop insurance, peaches, revenue insurance, yield insurance, Risk and Uncertainty,

Harmonic strain-optical response revealed in the isotropic (liquid) phase of liquid crystals

International audienceA strong optical birefringence is observed when applying a small amplitude oscillatory strain to theliquid phase of a liquid crystal. This unpredicted birefringence is found to oscillate at the samefrequency as the driving frequency, with frequencies down to 0.01 Hz. This birefringence is visibleup to 15 C above the liquid crystal transition. This opto-dynamic property is interpreted as a resultof a coupling of the orientational pretransitional fluctuations existing in the isotropic phase andlong range elastic interactions recently identified in liquids. The conversion of the mechanicalwave in an optical response is shapeable. Two examples of synchronized periodic signals areshown: the sine and the square waves. The optimization of the signal is analyzed using aHeaviside-step shear test. This optical property is immediately exploitable to design low energyon/off switching material

Hidden solidlike properties in the isotropic phase of the 8CB liquid crystal

International audienceNovel dynamic experiments have enabled the identification of a macroscopic solidlike response in the isotropic phase of a low molecular weight liquid crystal, 4,4'-n-octylcyanobiphenyl (8CB). This unknown property indicates that the low frequency shear elasticity identified in the isotropic phase of liquid crystal polymers is not reminiscent from the glass transition but reveals likely a generic property of the liquid state. The comparison to high molecular weight liquid crystals indicates, however, that the shear modulus is much enhanced when the liquid crystal moieties are attached to a polymer chain. The macroscopic length scales probed (0.050–0.100 mm) exclude wall-induced effects. DOI: 10.1103/PhysRevE.88.050501 PACS number(s): 61.30.Hn, 68.08.−p, 87.15.hg, 83.85.Vb The knowledge of the timescales involved in liquid crystalline systems is of outmost importance to understand, control, and improve their characteristics. The submillimeter scales properties attract a tremendous research interest [1–4]. However, few studies concern the isotropic phase away from pretransitional effects. Assimilated to ordinary viscous liquids, the isotropic phase is not supposed to exhibit solidlike properties, or at very high frequency only (mega-or gigahertz) as ordinary liquids. For this reason, the low frequency behavior of the isotropic phase remains mistakenly unexplored. Experimentally, the viscous or solidlike nature of a material is deduced from its response to a low frequency mechanical solicitation. A couple of years ago, careful dynamic experiments carried out in the isotropic phase of high molecular weight liquid crystals [side-chain liquid crystalline polymers (SCLCPs)] have revealed an as-yet unknown property: the isotropic melt does not flow but exhibits a finite shear elasticity of about several thousand Pascals at low frequency (0.1–10 Hz) [5–9]. The identification of low frequency shear elasticity in the isotropic phase of SCLCPs away from the isotropic-nematic transition opens numerous questions on the origin of this new property. It neither seems to result from the contribution of the liquid crystal moieties nor from surface anchoring effects, but likely from a generic property of the liquid state. Measurable in SCLCPs at macroscopic length scales as far as 100 • away from the glass transition temperature [5,7,9], the shear elasticity of SCLCPs still raises the debated question of reminiscent glass transition effects. In this Rapid Communication, we probe the dynamic properties of the low molecular counterpart: the 4,4'-n-octylcyanobiphenyl (8CB). The widely studied molecule can be considered as a representative liquid crystal molecule. 8CB exhibits a crystalline phase at low temperatures that enables one to rule on the question of pretransitional glass transition effects. We reveal a low frequency, solidlike response at several tens of micrometers sample thickness in the isotropic phase of 8CB, meaning that long range correlations are preserved when the orientational order is lost. This shear elasticity is detectable if special attention is paid to boundary conditions between the substrate and the sample. Under these conditions, the shear stress is optimally transmitted between the sampl

Thermodynamically self-consistent liquid state theories for systems with bounded potentials

The mean spherical approximation (MSA) can be solved semi-analytically for the Gaussian core model (GCM) and yields - rather surprisingly - exactly the same expressions for the energy and the virial equations. Taking advantage of this semi-analytical framework, we apply the concept of the self-consistent Ornstein-Zernike approximation (SCOZA) to the GCM: a state-dependent function K is introduced in the MSA closure relation which is determined to enforce thermodynamic consistency between the compressibility route and either the virial or energy route. Utilizing standard thermodynamic relations this leads to two different differential equations for the function K that have to be solved numerically. Generalizing our concept we propose an integro-differential-equation based formulation of the SCOZA which, although requiring a fully numerical solution, has the advantage that it is no longer restricted to the availability of an analytic solution for a particular system. Rather it can be used for an arbitrary potential and even in combination with other closure relations, such as a modification of the hypernetted chain approximation.Comment: 11 pages, 11 figures, submitted to J. Chem. Phy