Optimization of Dimensions of Cylindrical Piezoceramics as Radio-Clean Low Frequency Acoustic Sensors

Circular piezoelectric transducers with axial polarization are proposed as low frequency acoustic sensors for dark matter bubble chamber detectors. The axial vibration behaviour of the transducer is studied by three different methods: analytical models, FEM simulation, and experimental setup. To optimize disk geometry for this application, the dependence of the vibrational modes in function of the diameter-to-thickness ratio from 0.5 (a tall cylinder) to 20.0 (a thin disk) has been studied. Resonant and antiresonant frequencies for each of the lowest modes are determined and electromechanical coupling coefficients are calculated. From this analysis, due to the requirements of radiopurity and little volume, optimal diameter-to-thickness ratios for good transducer performance are discussed.

High Resolution Piezoresponse Force Microscopy Study of Self-Assembled Peptide Nanotubes

ABSTRACT Peptide nanotubes based on short dipeptide diphenylalanine (FF) attract a lot of attention due to their unique physical properties ranging from strong piezoelectricity to extraordinary mechanical rigidity. In this work, we present the results of high-resolution Piezoresponse Force Microscopy (PFM) measurements in FF microtubes prepared from the solution. First in-situ temperature measurements show that the effective shear piezoelectric coefficient d15 (proportional to axial polarization) significantly decreases (to about half of the initial value) under heating up to 100 oC. The piezoresponse becomes inhomogeneous over the surface being higher in the center of the tubes. Further, PFM study of a composite consisting of FF microtubes and reduced graphene oxide (rGO) was performed. We show that piezoelectric properties of peptide microtubes are significantly modified and radial (vertical) piezoresponse appears in the presence of rGO as confirmed via PFM analysis. The results are rationalized in terms of molecular approach in which π – π molecular interaction between rGO and dipeptide is responsible for the appearance of radial component of polarization in such hybrid structures.

The Dachsous/Fat/Four-jointed pathway implements axial long-range cell orientation

SUMMARYDespite a cumulative body of knowledge describing short-range cell interactions in morphogenetic processes, relatively little is known on the mechanism involved in the long-range spatial and temporal coordination of cells to build functional and structurally organized tissues. In particular, the attainment of a functionally optimized epithelia must require directional cues to instruct cell movements and cell orientations throughout the tissue field. In Drosophila, the adult epidermis of the abdominal segments is created de novo by the replacement of obsolete larval epidermal cells (LECs) by histoblasts (imaginal founder cells). As these proliferate, expand and fuse, they uniformly organize orienting on the surface along the antero-posterior axis. We found that the coordinated, axially oriented changes in shape of histoblasts respond to a dynamic, yet stereotyped redesign of the epithelial field mediated by the Dachsous/Fat/Four-jointed (Ds/Ft/Fj) pathway. The establishment and refinement of the expression gradients of the atypical cadherins Ds and Ft result in their axial polarization across cell interfaces and differential adhesiveness. We suggest that the role of Ds/Ft/Fj in long-range axially oriented planar cell alignment is a general function and that the regulation of the expression of its components would be crucial in the achievement of tissue uniformity in many other morphogenetic models or during tissue repair.

Non-canonical Wnt signalling modulates the endothelial shear stress flow sensor in vascular remodelling

Endothelial cells respond to molecular and physical forces in development and vascular homeostasis. Deregulation of endothelial responses to flow-induced shear is believed to contribute to many aspects of cardiovascular diseases including atherosclerosis. However, how molecular signals and shear-mediated physical forces integrate to regulate vascular patterning is poorly understood. Here we show that endothelial non-canonical Wnt signalling regulates endothelial sensitivity to shear forces. Loss of Wnt5a/Wnt11 renders endothelial cells more sensitive to shear, resulting in axial polarization and migration against flow at lower shear levels. Integration of flow modelling and polarity analysis in entire vascular networks demonstrates that polarization against flow is achieved differentially in artery, vein, capillaries and the primitive sprouting front. Collectively our data suggest that non-canonical Wnt signalling stabilizes forming vascular networks by reducing endothelial shear sensitivity, thus keeping vessels open under low flow conditions that prevail in the primitive plexus.