Ring-Pattern Dynamics in Smectic-C* and Smectic-C_A* Freely Suspended Liquid Crystal Films

Ring patterns of concentric 2pi-solitons in molecular orientation, form in freely suspended chiral smectic-C films in response to an in-plane rotating electric field. We present measurements of the zero-field relaxation of ring patterns and of the driven dynamics of ring formation under conditions of synchronous winding, and a simple model which enables their quantitative description in low polarization DOBAMBC. In smectic C_A* TFMHPOBC we observe an odd-even layer number effect, with odd number layer films exhibiting order of magnitude slower relaxation rates than even layer films. We show that this rate difference is due to much larger spontaneous polarization in odd number layer films.Comment: 4 RevTeX pgs, 4 eps figures, submitted to Phys. Rev. Let

Distinct degassing pulses during magma invasion in the stratified Karoo Basin – New insights from hydrothermal fluid flow modelling

Magma emplacement in organic‐rich sedimentary basins is a main driver of past environmental crises. Using a 2D numerical model, we investigate the process of thermal cracking in contact aureoles of cooling sills and subsequent transport and emission of thermogenic methane by hydrothermal fluids. Our model includes a Mohr‐Coulomb failure criterion to initiate hydrofracturing and a dynamic porosity/permeability. We investigate the Karoo Basin, taking into account host‐rock material properties from borehole data, realistic total organic carbon content, and different sill geometries. Consistent with geological observations, we find that thermal plumes quickly rise at the edges of saucer‐shaped sills, guided along vertically fractured high permeability pathways. Contrastingly, less focused and slower plumes rise from the edges and the central part of flat‐lying sills. Using a novel upscaling method based on sill‐to‐sediment ratio we find that degassing of the Karoo Basin occurred in two distinct phases during magma invasion. Rapid degassing triggered by sills emplaced within the top 1.5 km emitted ~1.6·103 Gt of thermogenic methane, while thermal plumes originating from deeper sills, carrying a 12‐times greater mass of methane, may not reach the surface. We suggest that these large quantities of methane could be re‐mobilized by the heat provided by neighboring sills. We conclude that the Karoo LIP may have emitted as much as ~22.3·103 Gt of thermogenic methane in the half million years of magmatic activity, with emissions up to 3 Gt/year. This quantity of methane and the emission rates can explain the negative δ13C excursion of the Toarcian environmental crisis. Key Points Sill geometry and emplacement depth as well as intruded host rock type are the main factors controlling methane mobilization and degassing Dehydration‐related porosity increase and pore‐pressure‐induced hydrofracturing are important mechanisms for a quick transport of methane from sill to the surface The Karoo Basin may have degassed ~22.3·103 Gt of thermogenic methane in the half million years of magmatic activit

Texton Noise

Designing realistic noise patterns from scratch is hard. To solve this problem, recent contributions have proposed involved spectral analysis algorithms that enable procedural noise models to faithfully reproduce some class of textures. The aim of this paper is to propose the simplest and most efficient noise model that allows for the reproduction of any Gaussian texture. Texton noise is a simple sparse convolution noise that sums randomly scattered copies of a small bilinear texture called texton. We introduce an automatic algorithm to compute the texton associated with an input texture image that concentrates the input frequency content into the desired texton support. One of the main features of texton noise is that its evaluation only consists to sum thirty texture fetches on average. Consequently texton noise generates Gaussian textures with an unprecedented evaluation speed for noise by example. A second main feature of texton noise is that it allows for high quality on-the-fly anisotropic filtering by simply invoking existing GPU hardware solutions for texture fetches. In addition, we demonstrate that texton noise can be applied on any surface using parameterization-free surface noise and that it allows for noise mixing

Pseudo-lamellar ordering in uniaxial and biaxial lyotropic nematics : a synchrotron X-ray diffraction experiment

Synchrotron X-ray measurements are performed in both uniaxial (discotic and calamitic) and biaxial nematic lyomesophases of the mixture K-laurate, 1-decanol and D2O. A first-order band and a second-order band with spacing ratio 1 : 2 characteristic of a pseudo-lamellar structure are observed in the three nematic phases. The X-ray diffraction results are interpreted in terms of the orientational fluctuations of intrinsically biaxial correlation volumes. It is argued that the calamitic and discotic phases are not built up of cylindric-like and disk-like micelles, but of aggregates of statistically biaxial shape, similar in the three nematic phases. The only change at the uniaxial-biaxial nematic transitions is the long-range order.Des mesures sont réalisées aux rayons X du synchrotron de LURE sur les phases lyotropes nématiques, uniaxes (discotiques et calamitiques) et biaxes, d'un mélange de laurate de potassium, 1-décanol et D2O. Dans les trois phases, on observe le premier et le second ordre d'une bande de diffraction caractéristique d'une structure pseudo-lamellaire. Les clichés de diffraction X sont interprétés en termes de fluctuations orientationnelles de volumes de corrélations intrinsèquement biaxes. On en déduit que les phases calamitiques et discotiques ne sont pas composées de micelles cylindriques (ou en forme de disques), mais d'agrégats de forme statistiquement biaxe, semblable dans les trois phases nématiques. Seul l'ordre à longue distance change aux transitions nématiques uniaxes-biaxes

Structural and optical investigations of TGB A and TGB C mesophases exhibiting cylindrical and cone-like domain textures

PACS. 61.30.-v Liquid crystals,

Macrocanonical Models for Texture Synthesis

In this article we consider macrocanonical models for texture synthesis. In these models samples are generated given an input texture image and a set of features which should be matched in expectation. It is known that if the images are quantized, macrocanonical models are given by Gibbs measures, using the maximum entropy principle. We study conditions under which this result extends to real-valued images. If these conditions hold, finding a macrocanonical model amounts to minimizing a convex function and sampling from an associated Gibbs measure. We analyze an algorithm which alternates between sampling and minimizing. We present experiments with neural network features and study the drawbacks and advantages of using this sampling scheme

Experimental investigations of a new TGBc mesophase

We report on optical and structural X-ray studies on a smectic C twist grain boundary phase (TGBC) of a pure liquid crystalline material. It is shown that this TGBC phase, which exists over a large range of temperature, is definitely different from previously reported and predicted TGBC phases. The two main experimental features are: (i) the observation in planar geometry of an optical texture exhibiting a square grid pattern, and (ii) the detection of a broad Bragg ring in reciprocal space instead of one (TGBA) or two (TGBC) sharp rings. We suggest a few possible tracks that can be explored to understand the complex structure of this new phase

Diversity of spoilage fungi in dairy products and environment, and their resistance to chemical preservatives

Fungal spoilage is one of the causes of consequential losses in the dairy industry. In this context, the use of bioprotective cultures can be an alternative or a complementary approach to be considered. Lactic acid bacteria (LAB) and propionibacteria, as well as some fungal species, can exhibit antifungal activities with large differences in activity between strains. Therefore, it is necessary to develop high-throughput screening methods to test a large number of strains and find the most efficient ones. In the present study, we developed a miniaturized high-throughput screening technique to rapidly detect antifungal activities in a cheese-like model. This model, distributed in a 24-well plate, consisted of 5-fold concentrated whole milk ultrafiltration retentate (final fat concentration of 45%), rennet (0.03%) and inoculated with a mesophilic lactic commercial starter and a pH indicator. Each well of the plate could be considered as a miniature cheese of ~2 g. Potent antifungal isolates were cultured in two dairy media; (i) a 10%-reconstituted low heat skim milk supplemented with 45% anhydrous milk fat (LH) and (ii) a 6-fold concentrated milk ultrafiltration permeate sterilized by 0.22 μm filtration and complemented with 10 g/l yeast extract and a pH indicator (UF). After cultivation, cultures (100 µl) were deposited on the miniature cheese surfaces followed by inoculation in duplicate with 50 spores or cells of 4 different fungal targets (1 fungi/plate), e.g., Mucor racemosus, Galactomyces geotrichum, Penicillium commune and Yarrowia lipolytica, and incubation at 12°C for up to 15 days. We screened 505 bacterial isolates belonging to Lactobacillus, Lactococcus, Pediococcus, Leuconostoc and Propiobacterium genera and 198 fungal isolates belonging to 28 genera. This high-throughput screening for antifungal activity revealed that 52 and 216 bacteria, and, 53 and 89 fungi, inhibited at least one fungal target after cultivation in UF and LH, respectively. Among the 4 tested fungal targets, P. commune was the most frequently inhibited fungus while only few isolates were able to inhibit M. racemosus or Y. lipolytica. This method opens new possibilities to screen microorganisms for antifungal activities. These results also underline the importance of the culture and screening media used on the expression of antifungal activities by bacteria or fungi