Dense pedestrian crowds versus granular packings: An analogy of sorts

Analogies between the dynamics of pedestrian crowds and granular media have long been hinted at.They seem all the more promising as the crowd is (very) dense, in which case the mechanical constraints prohibiting overlapsmight prevail over the decisional component of pedestrian dynamics. These analogies and their origins are probed in two distinct settings, (i) a flow through a narrow bottleneck and (ii) crossing of a static assembly by an intruder. Several quantitative similarities have been reported for the former setting and are discussed here, while setting (ii) reveals discrepancies in the response pattern, which areascribed to the pedestrians' ability to perceive, anticipate and self-propel

Steering self-organisation through confinement

Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self-organisation of soft-matter systems and identify overarching scientific challenges that need to be addressed to harness its full scientific and technological potential in soft matter and related fields. By drawing analogies with other disciplines, this framework will accelerate a common deeper understanding of self-organisation and trigger the development of innovative strategies to steer it using confinement, with impact on, e.g., the design of smarter materials, tissue engineering for biomedicine and in guiding active matter

Optical evidence of the layered array of grain boundaries in TGBA_{\rm A} and TGBC_{\rm C} mesophases

We report optical pitch measurements on chiral mesophases : cholesteric, twist grain boundary smectic (TGB$_{\rm A}$ and TGB$_{\rm C}$) and helicoidal smectic C. The nature of the phase transitions is discussed. A new series of defect lines parallel to the usual Grandjean-Cano steps is observed in the TGB phases only. They are interpreted as edge dislocations of the layered array of smectic slabs stacked along the TGB screw axis and thus as a direct visual evidence of the Renn-Lubensky structure. Their origin and stability are discussed in an elastic model of strain of a TGB sample. Their core is described as a wall constituted of edge dislocation lines.Nous présentons des mesures optiques de pas d'hélice dans des mésophases chirales cholestérique, smectiques torsadés par joints de grain (TGB$_{\rm A}$ et TGB$_{\rm C}$) et smectique C hélicoidal. Cette étude permet de discuter l'ordre des transitions de phases. De nouvelles lignes de défauts parallèles aux lignes de Grandjean-Cano sont observées dans les phases TGB uniquement. Elles sont interprétées comme des dislocations de l'empilement régulier des parois de joints de grain et donc comme une visualisation directe de leur existence. Leur origine et leur stabilité sont discutées grâce à un modèle élastique de déformation d'un TGB sous contrainte. Leur coeur est décrit comme une paroi formée de lignes de dislocations coin

S20 photocathodes grown by molecular-beam deposition

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TGBA_{\rm A} and TGBC_{\rm C} phases in some chiral tolan derivatives

Three chiral compounds ($n=10, 11, 12$) belonging to the optically active series : 3-fluoro-4-[(R) or (S)-1-methylheptyloxy]-4$'$-(4$''$-alkoxy-2$''$, 3$''$-difluorobenzoyloxy) tolans ($n$F$_{2}$BTFO$_{1}$M$_{7}$) have been synthesized. The helical S$_{\rm A}^{*}$ phase or TGB$_{\rm A}$ phase is found in the decyloxy derivative. The most interesting compound is obtained with $n=11$. It displays, for the first time, two TGB phases (TGB$_{\rm A}$ and TGB$_{\rm C}$ phases). The nature of these helical smectic phases is confirmed by different studies : optical observation, DSC, contact method, mixtures, X-ray diffraction and helical pitch measurements. the electrooptical properties of the S$_{\rm C}^{*}$ phase have also been studied.Trois produits ($n=10, 11, 12$) de la série chirale : 3-fluoro-4-[(R) ou (S)-1-methylheptyloxy]-4$'$-(4$''$-alcoxy-2$''$, 3$''$-difluorobenzoyloxy) tolanes ($n$F$_{2}$BTFO$_{1}$M$_{7}$) ont été synthétisés. Les deux premiers produits présentent la phase S$_{\rm A}^{*}$ hélicoïdale ou torse (TGB$_{\rm A}$). L'existence de la nouvelle phase TGB$_{\rm C}$, prédite par Renn et Lubensky, a été trouvée dans les deux derniers matériaux et prouvée par plusieurs études : observation microscopique, AED, méthode de contact, mélanges binaires, diffraction de rayons X et mesures du pas d'hélice. Le diagramme de phase réalisé entre ces trois matériaux est similaire à celui prédit par Renn. Les propriétés électrooptiques de la phase S$_{\rm C}^{*}$ ferroélectrique ont aussi été étudiées

HIV-1 gp120 induces an association between CD4 and the chemokine receptor CXCR4.

For efficient entry into target cells, certain T cell-tropic HIV-1 isolates require both CD4 and the coreceptor CXCR4. However, the molecular interactions among CD4, CXCR4, and the HIV-1 envelope glycoproteins are only now being elucidated. Here we show that the binding of soluble gp120 from one macrophage-tropic and four T cell-tropic viruses to a CD4+, but not to a CD4-, T cell line, decreased the binding of an mAb specific for CXCR4 to its epitope, implying an interaction among gp120, CD4, and CXCR4. To confirm such an interaction, we conducted double- and triple-color confocal laser scanning microscopy on CD4+/CXCR4+ cells and determined the extent of CD4 and CXCR4 colocalization by a semiquantitative analysis. In the absence of gp120, a low level of constitutive colocalization between CD4 and CXCR4 was observed. Treatment with T cell-tropic-derived gp120 and, to a lesser extent, macrophage-tropic-derived gp120, increased the colocalization of CD4 with CXCR4, and triple staining indicated that gp120 was associated with the CD4-CXCR4 complexes. Cocapping of the gp120-CD4-CXCR4 complexes at 37 degrees C resulted in the cointernalization of a proportion of the gp120-CXCR4 complexes into intracellular vesicles. These data demonstrate that the binding of gp120 to CD4+ T cells induces the formation of a trimolecular complex consisting of gp120, CD4, and the HIV-1 coreceptor molecule CXCR4

Polarization periodicity in the B1 columnar phase determined by resonant x-ray scattering

We report structural results that evidence the polarization distribution of the blocks in the columnar phase of an achiral bent-core liquid crystal. The study was performed using resonant x-ray diffraction at the sulfur K edge on oriented samples aligned on substrates. The extra periodicity is revealed through the violation of the systematic extinction rule of the structural symmetry group along the experimentally accessible diffraction direction. Further data obtained from the polarization analysis of a resonant reflection give information concerning the transition mechanism between B1 and B2 phases

Core-rod myopathy caused by mutations in the nebulin gene

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