Shear Alignment and Instability of Smectic Phases

We consider the shear flow of well-aligned one-component smectic phases, such as thermotropic smectics and lamellar diblock copolymers, below the critical region. We show that, as a result of thermal fluctuations of the layers, parallel ($c$) alignment is generically unstable and perpendicular ($a$) alignment is stable against long-wavelength undulations. We also find, surprisingly, that both $a$ and $c$ are stable for a narrow window of values for the anisotropic viscosity.Comment: To appear in PRL. Revtex, 1 figure

DNA methylation patterns of Brachypodium distachyon chromosomes and their alteration by 5-azacytidine treatment

Sequential immunolocalisation of 5-methylcytosine (5-MeC) and fluorescence in situ hybridisation with chromosome-specific BAC clones were performed on Brachypodium distachyon mitotic metaphase chromosomes to determine specific DNA methylation patterns of each chromosome in the complement. In the majority of cells examined, chromosomes Bd4 and Bd5, which bear the loci of 5S and 35S ribosomal DNA, respectively, had characteristic 5-MeC patterns. In contrast, the distribution of 5-MeC along the metacentric chromosome pairs Bd1, Bd2 and Bd3 was more variable. There were numerous differences in distribution of methylated sites between homologous chromosomes as well as between chromosome arms. Some chromosome sites, such as pericentromeric regions, were highly methylated in all chromosomes. Additionally, the influence of a hypomethylating agent, 5-azacytidine, on B. distachyon chromosome methylation patterns was confirmed. It was found that some chromosome pairs underwent demethylation more easily than others, but there was no apparent regularity in demethylation of particular chromosome segments

Tractability in Constraint Satisfaction Problems: A Survey

International audienceEven though the Constraint Satisfaction Problem (CSP) is NP-complete, many tractable classes of CSP instances have been identified. After discussing different forms and uses of tractability, we describe some landmark tractable classes and survey recent theoretical results. Although we concentrate on the classical CSP, we also cover its important extensions to infinite domains and optimisation, as well as #CSP and QCSP

Możliwości ograniczenia zawartości formaldehydu w płytach wiórowych do poziomu charakteryzującego drewno naturalne

The article presents the results of research on the influence of selected technological parameters, changed within a range similar to values presently used in industry, on the properties of three-layer particleboards produced from pine particlesobtained from sawmill waste. The particles were glued with amine resins. The panels, produced using urea-formaldehyde resin modified with melamine, were characterisedby the lowest content of formaldehyde, i.e. below 2 mg/100 g of ovendry board, after conversion into a value corresponding to the moisture content of the panels equalling 6.5%. The emissions of formaldehyde determined by the chamber and gas analysis methods were much lower than the threshold values recommended in international regulations and used as a basis for the classification of particleboards.W artykule przedstawiono wyniki badań wpływu wybranych parametrów technologicznych, zmienianych w przedziale zbliżonym do wartości aktualnie stosowanych w przemyśle, na właściwości trzywarstwowych płyt wiórowych wytwarzanych z wiórów sosnowych pozyskanych z odpadów tartacznych. Do zaklejania wiórów stosowano żywice aminowe. Najmniejszą zawartością formaldehydu, poniżej 2 mg/100g zupełnie suchej płyty, po przeliczeniu na wartość odpowiadającą wilgotności płyt – 6,5%, charakteryzowały się płyty wytworzone z żywicą mocznikowo-formaldehydową modyfikowaną melaminą. Emisja formaldehydu badana metoda komorową i analizy gazowej była znacznie mniejsza od wartości granicznych, obowiązujących i proponowanych w przepisach międzynarodowych, jako podstawa klasyfikacji płyt wiórowych

On the degrees of permutability of subregular varieties

summary:An algebra ${\mathcal A}= (A,F)$ is subregular alias regular with respect to a unary term function $g$ if for each $\Theta , \Phi \in \text{Con}\,{\mathcal A}$ we have $\Theta = \Phi$ whenever $[g(a)]_{\Theta } = [g(a)]_{\Phi }$ for each $a\in A$. We borrow the concept of a deductive system from logic to modify it for subregular algebras. Using it we show that a subset $C\subseteq A$ is a class of some congruence on $\Theta$ containing $g(a)$ if and only if $C$ is this generalized deductive system. This method is efficient (needs a finite number of steps)

Alignment of Complex Fluids under Confinement and Flow

We report on a new application of the X-ray Surface Forces Apparatus [1-4] (XSFA) to the study of the alignment of complex fluid thin films under confinement and/or flow using synchrotron X-ray scattering. The smectic A liquid crystal 8CB (4-cyano-4${'}$-octylbiphenyl) and the hexagonal phases of a zwitterionic polyisoprene melt and of a lyotropic liquid crystal composed of sodium dodecyl sulfate (SDS), pentanol and water were investigated in the regime where the distances between the confining surfaces range from 0.4 to tens of microns. In this paper, we demonstrate that this new technique allows preparation of highly-oriented complex fluid samples suitable for high resolution X-ray diffraction and scattering studies. In addition, we have directly measured forces across thin films of 8CB using the conventional Surface Forces Apparatus (SFA). The force measurements complement well the direct X-ray imaging and provide indirect information on the sample alignment in films a few tens of Ångströms thick