A method was developed for the rapid determination coumatetralyl in cola- and orange-type soft drinks, which includes extraction using solid-matrix column, clean-up by silica cartridge chromatography ...and reversed-phase high-performance liquid chromatography with diode-array detection. The recovery of coumatetralyl from 50 ml of soft drinks was better than 80% at spiking levels down to 50 micrograms/kg (ppb).
Based on the classical theory of simple materials of differential type and the results on the analytical form of constitutive models consistent with the laws of thermodynamics, we introduce a very ...general response function for the Cauchy stress tensor of a dispersive hyperelastic solid. Next, by focusing on the propagation of localised waves in slightly dispersive quasi incompressible solids, we prove the existence of a rich variety of solitary wave solutions as well as kink wave solutions. Our analysis and results can be easily specialised to shape memory alloys.
Display omitted
•We develop a mathematical model for the stress tensor of dispersive hyperelastic solids within the theory of simple materials of differential type.•We study the wave propagation in dispersive hyperelastic solids.•In the small but finite regime, we find exact solutions representing solitary and kink waves.
When nematic liquid crystals are constrained to a curved surface, the geometry induces distortions in the molecular orientation. The mechanisms of the geometrical frustration involve the intrinsic as ...well as the extrinsic geometry of the underlying substrate. We show that the nematic elastic energy promotes the alignment of the flux lines of the nematic director towards geodesics and/or lines of curvature of the surface. As a consequence, the influence of the curvature can be tuned through the Frank elastic moduli. To illustrate this effect, we consider the simple case of nematics lying on a cylindrical shell. By combining the curvature effects with external magnetic fields, the molecular alignment can be reoriented or switched between two stable configurations. This enables the manipulation of nematic alignment for the design of new materials and technological devices.
Cultural tourism is recognized as one of the main resources used to counteract seasonality in tourist destinations, being by its very nature non-seasonal. Moreover, according to the generally ...accepted stereotype, cultural tourists tend to be ageing and therefore more likely to travel also during the off-peak season than younger tourists. Our data show that international cultural tourism has increased in Italy during the last 15 years, but this increase has not contributed to reducing seasonality. We have conducted a statistical analysis of the data in an attempt to explore the possible reasons behind such an unexpected finding. By comparing foreign cultural and non-cultural tourists through several socio-economic-demographic variables, our results highlight the fact that a “new (and younger) cultural tourism” is emerging in Italy. Consequently, promoting cultural tourism is just one component for effectively counteracting seasonality. Nevertheless, promotion should also focus on the dual concept of “cultural tourism/ageing tourists”.
•Cultural tourism has increased in Italy, but seasonality has not reduced.•To understand why, the characteristics of cultural and non-cultural tourists are compared.•Data confirm that cultural tourism is the less seasonal form of international tourism.•Age is the key factor. A younger cultural tourism is emerging in Italy.•Cultural tourism should be promoted to ageing tourists to reduce seasonality.
The Rayleigh–Bénard problem in viscous fluids is one of the most intensely studied problems in fluid mechanics. The literature is rich in studies concerning Navier–Stokes fluids with constant ...material properties and fluids with variable viscosity and/or thermal conduction, whereas it lacks in results concerning the more realistic case in which all the material properties of the fluid are variable. In this paper, we re-examine the classical problem of the onset of thermal-convection for fluids whose material properties depend on the pressure and temperature by studying the linear stability of the conduction solution.
We derive the hydrodynamic equations for nematic liquid crystals lying on curved substrates. We invoke the Lagrange-Rayleigh variational principle to adapt the Ericksen-Leslie theory to ...two-dimensional nematics in which a degenerate anchoring of the molecules on the substrate is enforced. The only constitutive assumptions in this scheme concern the free-energy density, given by the two-dimensional Frank potential, and the density of dissipation which is required to satisfy appropriate invariance requirements. The resulting equations of motion couple the velocity field, the director alignment, and the curvature of the shell. To illustrate our findings, we consider the effect of a simple shear flow on the alignment of a nematic lying on a cylindrical shell.
The paper analyzes the effects of air transport deregulation on international tourism flows in the Italian regions. Due to several reasons, tourist flows rarely are equally distributed within a ...nation. We focus on the accessibility to a territory as one of those reasons. Easy and cheap access to a destination is the prerequisite for its tourism development; in this respect, the advent of low-cost carriers has increased accessibility to many tourist destinations. We propose a segmented regression analysis to study the evolution of the share of European tourist arrivals in each region on the total European tourists visiting Italy. Accordingly, we identify which regions have gotten a higher advantage in terms of tourism growth due to the air transport deregulation.
•International tourist flows are not equally distributed among Italian regions.•Low-cost carriers have increased accessibility to many peripheral destinations.•The segmented regression model highlighted breakpoints in the trend.•The relative number of European tourists visiting southern regions by air augmented.
The equations of nonlinear elastodynamics have attracted the attention of pure and applied mathematicians since the second half of the last century. Nevertheless, many aspects of this theory are ...still obscure or need a more systematic analysis. In this paper we study the wave propagation in an isotropic elastic solid by taking into account the effects due to dispersion. Specifically, we determine a class of global (in both time and space) solutions, find exact solutions for longitudinal travelling waves within the fourth-order theory of elasticity, and derive two asymptotic reductions of the governing equations for waves of small amplitudes.
•We study the wave propagation in a nonlinear isotropic elastic solid by taking into account the effects due to dispersion. We determine a class of global (in both time and space) solutions.•We find exact solutions for longitudinal travelling waves within the fourth-order theory of elasticity.•We derive two asymptotic reductions of the governing equations for waves of small but finite amplitudes.
A vivid research on brain tissue has proven that in simple shear tests the relation between the shear stress and shear strain is linear for strains in a range which is significative in the ...physiological and pathological regime. Since Mooney–Rivlin materials satisfy this peculiar property when subjected to simple shear deformations, the celebrated mathematical model introduced first by Mooney, and then developed by Rivlin, has been often used to describe the mechanical behaviour of brain tissue. Recently, it has been shown that a most general strain energy density for incompressible isotropic elastic materials exhibiting a linear relationship between shear stress and shear strain in simple shear deformation consists of the sum of the Mooney–Rivlin model and an arbitrary function of the difference of the first two principal invariants of the deformation tensor. For this reason, a strain energy function of this form is called a generalised Mooney–Rivlin model. In this note we design theoretically a procedure aiming at the determination of the generalised Mooney–Rivlin model which fits best the experimental data.
•Pseudo-universal relations for a generalised Mooney–Rivlin (GMR) material.•Small-amplitude wave propagation in a GMR material.•Necessary conditions for an incompressible isotropic elastic material to be modelled as a GMR material.•Acoustic tensor of a GMR material.
PDF
