1,721,042 research outputs found
Revealing the polar nature of a ferroelectric nematic by means of circular alignment
Get PDFThe recent discovery of spontaneously polar nematic liquid crystals—so-called ferroelectric nematics—more than a century after the first discussions about their possible existence—has attracted large interest, both from fundamental scientific and applicational points of view. However, the experimental demonstration of such a phase has, so-far, been non-trivial. Here I present a direct method for the experimental verification of a ferroelectric nematic liquid crystal phase. The method utilizes a single sample cell where the two substrates are linearly and circularly rubbed, respectively, and the ferroelectric nematic phase (NF) is revealed by the orientation of the resulting disclination lines in the cell
Dynamically Tunable Optical Cavities with Embedded Nematic Liquid Crystalline Networks
Get PDFTunable metal–insulator–metal (MIM) Fabry–P\ue9rot (FP) cavities that can dynamically control light enable novel sensing, imaging\ua0and display applications. However, the realization of dynamic cavities incorporating stimuli-responsive materials poses a significant engineering challenge. Current approaches rely on refractive index modulation and suffer from low dynamic tunability, high losses, and limited spectral ranges, and require liquid and hazardous materials for operation. To overcome these challenges, a new tuning mechanism employing reversible mechanical adaptations of a polymer network is proposed, and dynamic tuning of optical resonances is demonstrated. Solid-state temperature-responsive optical coatings are developed by preparing a monodomain nematic liquid crystalline network (LCN) and are incorporated between metallic mirrors to form active optical microcavities. LCN microcavities offer large, reversible and highly linear spectral tuning of FP resonances reaching wavelength-shifts up to 40\ua0nm via thermomechanical actuation while featuring outstanding repeatability and precision over more than 100 heating–cooling cycles. This degree of tunability allows for reversible switching between the reflective and the absorbing states of the device over the entire visible and near-infrared spectral regions, reaching large changes in reflectance with modulation efficiency ΔR\ua0=\ua079%
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Smectic LCD modes
No full textIn this article, we discuss display modes based on smectic liquid crystals with special focus on chiral tilted smectic materials. Here, we find the ferroelectric and antiferroelectric liquid crystals (FLCs and AFLCs) which can provide 100-1,000 times faster pixel switching than nematic LCs. The hysteretic switching of bistable surface-stabilized FLCs and AFLCs allows for passive matrix addressing, which made these materials the prime candidates for large direct view LCDs in the 1990s, before the active matrix thin-film-transistor (TFT) technology was mature enough to allow for large display panels. While FLCs have found a number of applications, no AFLC device has as yet been commercialized. With today’s large TFT-arrays - developed for nematic LCDs - there is an increasing interest in combining FLCs and AFLCs with active matrix technology, e.g., with the fast FLCs used in monostable, analog switching modes. This could lead to even more powerful LCDs with full grayscale and superior speed (facilitating field sequential color generation) compared to nematic LCDs
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Smectic LCD modes
No full text© Springer International Publishing Switzerland 2016.In this article, we discuss display modes based on smectic liquid crystals with special focus on chiral tilted smectic materials. Here, we find the ferroelectric liquid crystals and antiferroelectric liquid crystals (FLCs and AFLCs) which can provide 100-1,000 times faster pixel switching than nematic LCs. The hysteretic switching of bistable surface-stabilized FLCs and AFLCs allows for passive matrix addressing, which made these materials the prime candidates for large direct view LCDs in the 1990s, before the active-matrix thin-film transistor (TFT) technology was mature enough to allow for large display panels. While FLCs have found a number of applications, no AFLC device has as yet been commercialized. With today’s large TFT arrays - developed for nematic LCDs - there is an increasing interest in combining FLCs and AFLCs with active-matrix technology, e.g., with the fast FLCs used in monostable, analog switching modes. This could lead to even more powerful LCDs with full grayscale and superior speed (facilitating field sequential color generation) compared to nematic LCDs
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The Flexoelectro-Optic Effect in Cholesteric Liquid Crystals
No full textThe flexoelectrooptic effect in cholesteric liquid crystals is based on a linear coupling of the medium with an applied electric field. The electric field causes the optic axis, which is coinciding with the helix axis of the hardtwisted cholesteric (pitch < .lambda.), to rotate or tilt in a plane parallel to the cell glass plates. Hence, we have a uniaxial optical wave plate with a field-controlled direction of the optic axis, and essentially the same geometry as the electrooptic effects in the smectic C* phase (surface stabilized ferroelectric liquid crystals and deformed helielectrics) and the smectic A* (soft mode/electroclinic effect). This geometry, sometimes referred to as in-plane switching, guarantees a very wide viewing angle for displays and shutters. The field-induced tilt of the optic axis in the flexoelectrooptic effect is a linear function of the applied field which gives a well-controlled continuous grey-scale.<p /> The effect has been examined in its static as well as dynamic aspects. A general expression, describing the field-dependence of the tilt, containing the individual splay and bend flexoelectric coefficients and the three Oseen elastic constants was derived for the case of .DELTA..epsilon. = 0. It predicts a striking range of linearity of the induced tilt and furthermore that this tilt is temperature independent as long as the helical wave vector of the material is constant. In certain mixtures with .DELTA..epsilon. = 0 we have in fact reached induced tilt angles of more than 30 degrees without deviation from linearity. Moreover, a tilt angle of 22.5 degrees is enough for providing 100% light modulation.<p /> Several constant pitch cholesteric materials were investigated and our results confirm that the induced tilt of the optic axis is practically independent of temperature, which is a very attractive feature for applications. Moreover, the dynamics of the effect was studied. The electrooptic response is relatively fast, with response times of the order of 10.my.s to 100.my.s for the studied materials. We were also able to detect the immediate change in the flexoelectric coefficient due to a configurational change in the molecule, induced by light.<p /> We discuss the influence on the flexoelectrooptic effect of material parameters such as the flexoelectric coefficients, the elastic constants, and the dielectric anisotropy. The dielectric effect gives a non-linear contribution to the electrooptic response and we conclude that the dielectric anisotropy must be very close to zero in order to get a large linear response. The fittings and simulations based on the analysis conform very well with our experimental findings.<p /> So far, neither molecular materials nor alignment methods have been optimized for the flexoelectrooptic effect. The special uniform lying structure, of crucial importance for the effect, has a tendency to transform into Grandjean texture. We have solved this problem by creating a stabilizing polymeric network in the volume of the cell by means of photopolymerization of a small amount of reactive monomer added to the cholesteric.<p /> At the same time as proposing a simple method for measuring sign and magnitude of flexocoefficients, we finally point out the inconsistency of data reported so far regarding these coefficients in general and propose a standard convention of sign which hopefully will find international acceptance
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