Anisotropic random resistor networks: a model for piezoresistive response of thick-film resistors

A number of evidences suggests that thick-film resistors are close to a metal-insulator transition and that tunneling processes between metallic grains are the main source of resistance. We consider as a minimal model for description of transport properties in thick-film resistors a percolative resistor network, with conducting elements governed by tunneling. For both oriented and randomly oriented networks, we show that the piezoresistive response to an applied strain is model dependent when the system is far away from the percolation thresold, while in the critical region it acquires universal properties. In particular close to the metal-insulator transition, the piezoresistive anisotropy show a power law behavior. Within this region, there exists a simple and universal relation between the conductance and the piezoresistive anisotropy, which could be experimentally tested by common cantilever bar measurements of thick-film resistors.Comment: 7 pages, 2 eps figure

Longitudinal and transversal piezoresistive response of granular metals

In this paper, we study the piezoresistive response and its anisotropy for a bond percolation model of granular metals. Both effective medium results and numerical Monte Carlo calculations of finite simple cubic networks show that the piezoresistive anisotropy is a strongly dependent function of bond probability p and of bond conductance distribution width \Delta g. We find that piezoresistive anisotropy is strongly suppressed as p is reduced and/or \Delta g is enhanced and that it vanishes at the percolation thresold p=p_c. We argue that a measurement of the piezoresistive anisotropy could be a sensitive tool to estimate critical metallic concentrations in real granular metals.Comment: 14 pages, 7 eps figure

Experimental Characterization of a Multiple Spark Ignition System

Abstract The paper reports on the experimental analysis of a multiple spark ignition system, carried out with conventional and optical non intrusive methods. The system features a plug-top ignition coil with integrated electronics which delivers high ignition energy and high voltage compared to conventional ignition coils, and is capable of multiple discharges with reduced dwell time. The ignition system is characterized in terms of electrical parameters to evaluate the spark power and energy as a function of different hardware configurations and operating conditions. A high speed camera is used to visualize, at different ambient pressures, the time evolution of the electric arc discharge in order to highlight its position variability, which could have an impact on combustion kernel development and deflagration front stability in engines

Breaking the silence of the 500-year-old smiling garden of everlasting flowers: The En Tibi book herbarium

We reveal the enigmatic origin of one of the earliest surviving botanical collections. The 16th-century Italian En Tibi herbarium is a large, luxurious book with c. 500 dried plants, made in the Renaissance scholarly circles that developed botany as a distinct discipline. Its Latin inscription, translated as “Here for you a smiling garden of everlasting flowers”, suggests that this herbarium was a gift for a patron of the emerging botanical science. We follow an integrative approach that includes a botanical similarity estimation of the En Tibi with contemporary herbaria (Aldrovandi, Cesalpino, “Cibo”, Merini, Estense) and analysis of the book’s watermark, paper, binding, handwriting, Latin inscription and the morphology and DNA of hairs mounted under specimens. Rejecting the previous origin hypothesis (Ferrara, 1542–1544), we show that the En Tibi was made in Bologna around 1558. We attribute the En Tibi herbarium to Francesco Petrollini, a neglected 16th-century botanist, to whom also belongs, as clarified herein, the controversial “Erbario Cibo” kept in Rome. The En Tibi was probably a work on commission for Petrollini, who provided the plant material for the book. Other people were apparently involved in the compilation and offering of this precious gift to a yet unknown person, possibly the Habsburg Emperor Ferdinand I. The En Tibi herbarium is a Renaissance masterpiece of art and science, representing the quest for truth in herbal medicine and botany. Our multidisciplinary approach can serve as a guideline for deciphering other anonymous herbaria, kept safely “hidden” in treasure rooms of universities, libraries and museums

Spatio-Temporal Changes of Extracellular Matrix (ECM) Stiffness in the Development of the Leech Hirudo verbana

The invertebrate leech Hirudo verbana represents a powerful experimental animal model for improving the knowledge about the functional interaction between the extracellular matrix (ECM) and cells within the tissue microenvironment (TME), and the key role played by ECM stiffness during development and growth. Indeed, the medicinal leech is characterized by a simple anatomical organization reproducing many aspects of the basic biological processes of vertebrates and in which a rapid spatiotemporal development is well established and easily assessed. Our results show that ECM structural organization, as well as the amount of fibrillar and non-fibrillar collagen are deeply different from hatching leeches to adult ones. In addition, the changes in ECM remodelling occurring during the different leech developmental stages, leads to a gradient of stiffness regulating both the path of migratory cells and their fates. The ability of cells to perceive and respond to changes in ECM composition and mechanics strictly depend on nuclear or cytoplasmic expression of Yes-Associated Protein 1 (YAP1), a key mediator converting mechanical signals into transcriptional outputs, expression, and activation

Amyloid and allorecognition in the colonial ascidian Botryllus schlosseri.

Allorecognition, i.e., the ability of intraspecific nonself recognition is widely distributed among colonial, sessile marine organisms in the form of colony specificity. In the cosmopolitan compound ascidian Botryllus schlosseri, colony specificity is controlled by a highly polymorphic Fu/HC locus: two colonies sharing at least one alleleat the Fu/HC locus can fuse into a chimeric colony; if no alleles are shared, a typical inflammatory reaction occurs, with the recruitment of a specific hemocyte type, the cytotoxic morula cells (MCs), inside the tips of the ampullae (the blind termini ofthe tunic vasculature) extending towards the alien colony, their extravasation in the tunic and their final degranulation. As a consequence of allorecognition, necrotic, melanic spots (points of rejection; PORs) form along the contact border, due to the release, by MCs, of their granular content, mainly represented by quinones, polyphenols and the enzyme phenoloxidase (PO), upon the perception of the allogeneic humoral factors diffusing from the alien colony through the partially fused tunics. It is remarkable that the deposition of melanin and the cell death is confined to the immediate outside of the ampullar tips, suggesting that the diffusion of PO and the products of its activity are, in some way, prevented in order to limit cytotoxicity to the immediate neighbourhood of the contact region. In this context, we looked for factors released by MCs that could limit the spreading of cytotoxicity and melanisation. We found that MCs share with vertebrate melanocytes similar packaging of melanin precursors, entrapped in a 3Dscaffold of amyloid fibrils. They contribute to form the electron dense content of MC granules that, after stimulation, flake off and is released in the surrounding medium. Released amyloid fibrils limit the diffusion of the produced melanin. The search for genes and factor controlling both melanogenesis and amyloidogenesis, revealed an evolutionary conserved machinery involved in the processes and an unexpected cross talk between the two Botryllus immunocyte types, i.e., phagocytes and MCs. Furthermore, this work confirms the physiological role of amyloid in tunicate immunity