1,721,130 research outputs found
ELASTIC ANOMALIES AT THE INTERFACE BETWEEN A NEMATIC LIQUID-CRYSTAL AND ITS VAPOR - A MICROSCOPIC APPROACH
No full textClose to the interface between a nematic liquid crystal (NLC) and another medium the elastic constants are expected to become functions of distance z from the interface and of angle theta between the director n and the unit vector k orthogonal to the interface. Furthermore, due to symmetry breaking, new elastic contributions that are absent in the bulk may become important close to the interface. In this paper we consider a simple microscopic model based on van der Waals induced dipole-induced dipole interactions under the special assumption of perfect orientational order (S = 1). By using this model, we calculate the free energy density and the excess of surface free energy. Some elastic constants are obtained by using a numerical procedure. In particular, a new elastic contribution which is linear in the director gradients is obtained for the first time. Close to the interface, these elastic constants greatly depend on distance z and are simple functions of the scalar product n . k
An accurate optical method for measuring the azimuthal anchoring energy of nematic liquid crystals
No full textIn this paper we report an accurate optical method for measuring the azimuthal director angle and the azimuthal anchoring energy for a nematic liquid crystal. The method is fully automated and provides a direct measurement of the azimuthal angle. The experimental procedure exploits the dependence of the reflectivity tensor on the surface director orientation. The measurement of the azimuthal angle does not require any knowledge of the optical parameters of the nematic material or of the substrate, and provides an absolute accuracy better than 0.2 degrees in the whole range 0 degrees-360 degrees and a sensitivity of 0.01 degrees. If the optical parameters of both the nematic sample and the substrate are known, the surface polar angle can also be obtained from the experiment
Comment on “Humic substances extracted by alkali are invalid proxies for the dynamics and functions of organic matter in terrestrial and aquatic ecosystems,” by Kleber and Lehmann (2019)
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
CAPILLARITY EFFECTS ON SURFACE GRAVITY-WAVES IN A CYLINDRICAL CONTAINER - WETTING BOUNDARY-CONDITIONS
No full textSurface capillary-gravity waves are experimentally investigated in a cylindrical basin subjected to a horizontal oscillation by using a high-sensitivity optical method. We study the low-oscillation-amplitude regimes for a fluid which wets the vertical walls and we show that the presence of the capillary meniscus can effect greatly the main properties of the system. Both the free decay and the forced oscillations of surface oscillations are investigated. The amplitude, the phase and the damping of gravity waves are investigated in detail. The damping of the fundamental surface mode is found to exhibit nonlinear behaviour which is in qualitative agreement with the predictions of the Miles (1967) theory of capillary damping. The amplitude and the phase of gravity waves with respect to the oscillation of the container exhibit unusual behaviour which is strictly connected with the presence of the wetting boundary condition for the fluid at the vertical walls
Integrated use of local and technical soil quality indicators and participatory techniques to select them. A review of bib-liography and analysis of research strategies and outcomes
Full text linkClimate change has strong impacts on soil conservation and agricultural productivity, with severe consequences on smallholders in developing countries, but virtually no research has been carried out so far on this issue. Therefore, it is necessary to foster the implementation of participatory projects to help communities deal with new difficulties. Sustainable soil management can reduce and even reverse land degradation, helping farmers to adapt to climate change effects. Pro-gress toward sustainability cannot be implemented in small rural communities regardless of local knowledge, which can be addressed using participatory techniques. To this purpose the choice and use of indicators is essential to carry out correct assessments of soil vulnerability integrating local and technical knowledge. The purpose of this review was to study how the problem of building a set of integrated indicators to assess soil quality has been addressed so far and which participatory techniques have been more successfully employed, analyzing studies carried out in rural communities of developing countries. We found out that there is a lack of participated studies dealing with environmental issues. Those that do so address them only indirectly, being centered on present agricultural problems. The studies rarely feature a collaboration with social science experts, consequently the use of participatory techniques lacks protocols and a standardized nomenclature to help in the transfer and generalization of experiences. Women are rarely involved and nearly exclusively in African countries: this could be related to social and cultural conditions, but needs more atten-tion. Different aspects need to be improved to help the implementation of a successful approach in future projects. This review provides a tool to facilitate future interdisciplinary research on integration of local and scientific knowledge and will help to devise more successful strategies to tackle the challenges posed by climate change to smallholders in developing countries
EXPERIMENTAL-MEASUREMENT OF THE AZIMUTHAL ANCHORING ENERGY FUNCTION AT A SIO NEMATIC INTERFACE
No full textThe functional form of the azimuthal anchoring energy, i.e. the anisotropic part of the interfacial free energy, at the interface between the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl and an obliquely evaporated SiO substrate is measured for the first time by using a reflectometric method. The anchoring energy function is obtained by measuring the director rotation on the interface caused by an external magnetic field ranging from 0 to 2.3 T. The dependence of the anchoring energy on the director azimuthal angle is found to be well fitted by the function W(a)(phi) = W(a) sin2 phi in agreement with the predictions of the Berreman model for the anchoring at a grooved interface
- …
