297 research outputs found
A combined experimental/numerical study on the scaling of impact strength and toughness in composite laminates for ballistic applications
In this paper, the impact behaviour of composite laminates is investigated, and their potential for ballistic protection
assessed, as a function of the reinforcing materials and structure for three representative fibre-reinforced
epoxy systems involving carbon, glass, and para-aramid fibre reinforcements, respectively. A multiscale coupled
experimental/numerical study on the composite material properties is performed, starting from single fibre, to
fibre bundles (yarns), to single composite ply, and finally at laminate level. Uniaxial tensile tests on single fibres
and fibre bundles are performed, and the results are used as input for non-linear Finite Element Method (FEM)
models for tensile and impact simulation on the composite laminates. Mechanical properties and energy dissipation
of the single ply and multilayer laminates under quasi-static loading are preliminarily assessed starting from
the mechanical properties of the constituents and subsequently verified numerically. FEM simulations of ballistic
impact on multilayer armours are then performed, assessing the three different composites, showing good agreement
with experimental tests in terms of impact energy absorption capabilities and deformation/failure behaviour.
As result, a generalized multiscale version of the well-known Cuniff criterion is provided as a scaling law,
which allows to assess the ballistic performance of laminated composites, starting from the tensile mechanical
properties of the fibres and fibre bundles and their volume fraction. The presented multiscale coupled experimental-
numerical characterization confirms the reliability of the predictions for full-scale laminate properties starting
from the individual constituents at the single fibre scale
The Role of Trauma in Early Onset Borderline Personality Disorder: A Biopsychosocial Perspective
The role of childhood trauma in the development of borderline personality disorder (BPD) in young age has long been studied. The most accurate theoretical models are multifactorial, taking into account a range of factors, including early trauma, to explain evolutionary pathways of BPD. We reviewed studies published on PubMed in the last 20 years to evaluate whether different types of childhood trauma, like sexual and physical abuse and neglect, increase the risk and shape the clinical picture of BPD. BPD as a sequela of childhood traumas often occurs with multiple comorbidities (e.g. mood, anxiety, obsessive-compulsive, eating, dissociative, addictive, psychotic, and somatoform disorders). In such cases it tends to have a prolonged course, to be severe, and treatment-refractory. In comparison with subjects who suffer from other personality disorders, patients with BPD experience childhood abuse more frequently. Adverse childhood experiences affect different biological systems (HPA axis, neurotransmission mechanisms, endogenous opioid systems, gray matter volume, white matter connectivity), with changes persisting into adulthood. A growing body of evidence is emerging about interaction between genes (e.g. FKBP5 polymorphisms and CRHR2 variants) and environment (physical and sexual abuse, emotional neglect)
From Endogenous to Synthetic microRNA-Mediated Regulatory Circuits: An Overview
MicroRNAs are short non-coding RNAs that are evolutionarily conserved and are pivotal post-transcriptional mediators of gene regulation. Together with transcription factors and epigenetic regulators, they form a highly interconnected network whose building blocks can be classified depending on the number of molecular species involved and the type of interactions amongst them. Depending on their topology, these molecular circuits may carry out specific functions that years of studies have related to the processing of gene expression noise. In this review, we first present the different over-represented network motifs involving microRNAs and their specific role in implementing relevant biological functions, reviewing both theoretical and experimental studies. We then illustrate the recent advances in synthetic biology, such as the construction of artificially synthesised circuits, which provide a controlled tool to test experimentally the possible microRNA regulatory tasks and constitute a starting point for clinical applications
Evidence of light guiding in ion-implanted diamond
We demonstrate the feasibility of fabricating light-waveguiding microstructures in bulk single-crystal diamond by means of direct ion implantation with a scanning microbeam, resulting in the modulation of the refractive index of the ion-beam damaged crystal. Direct evidence of waveguiding through such buried microchannels is obtained with a phase-shift micro-interferometric method allowing the study of the multimodal structure of the propagating electromagnetic field. The possibility of defining optical and photonic structures by direct ion writing opens a range of new possibilities in the design of quantumoptical devices in bulk single-crystal diamond
Polarized micro-Raman studies of femtosecond laser written stress-induced optical waveguides in diamond
Understanding the physical mechanisms of the refractive index modulation
induced by femtosecond laser writing is crucial for tailoring the properties of
the resulting optical waveguides. In this work we apply polarized Raman
spectroscopy to study the origin of stress-induced waveguides in diamond,
produced by femtosecond laser writing. The change in the refractive index
induced by the femtosecond laser in the crystal is derived from the measured
stress in the waveguides. The results help to explain the waveguide
polarization sensitive guiding mechanism, as well as providing a technique for
their optimization.Comment: 5 pages, 4 figure
Computational modeling of the mechanics of hierarchical materials
Structural hierarchy coupled with material heterogeneity is often identifi ed in natural materials, from the nano- to the macroscale. It combines disparate mechanical properties, such as strength and toughness, and multifunctionality, such as smart adhesion, water repellence, self-cleaning, and self-healing. Hierarchical architectures can be employed in synthetic bioinspired structured materials, also adopting constituents with superior mechanical properties, such as carbon nanotubes or graphene. Advanced computational modeling is essential to understand the complex mechanisms that couple material, structural, and topological hierarchy, merging phenomena of different nature, size, and time scales. Numerical modeling also allows extensive parametric studies for the optimization of material properties and arrangement, avoiding time-consuming and complex experimental trials, and providing guidance in the fabrication of novel advanced materials. Here, we review some of the most promising approaches, with a focus on the methods developed by our group
Creation of pure non-crystalline diamond nanostructures via room-temperature ion irradiation and subsequent thermal annealing
Carbon exhibits a remarkable range of structural forms, due to the availability of sp3, sp2 and
sp1 chemical bonds. Contrarily to other group IV elements such as silicon and germanium,
the formation of an amorphous phase based exclusively on sp3 bonds is extremely
challenging due to the strongly favored formation of graphitic-like structures at room
19 temperature and pressure. As such, the formation of a fully sp3-bonded carbon phase requires
20 an extremely careful (and largely unexplored) definition of the pressure and temperature
across the phase diagram. Here, we report on the possibility of creating full-sp3 amorphous
nanostructures within the bulk crystal of diamond with room-temperature ion-beam
irradiation, followed by an annealing process that does not involve the application of any
external mechanical pressure. As confirmed by numerical simulations, the (previously
unreported) radiation-damage-induced formation of an amorphous sp2-free phase in diamond
is determined by the buildup of extremely high internal stresses from the surrounding lattice,
which (in the case of nanometer-scale regions) fully prevent the graphitization process.
Besides the relevance of understanding the formation of exotic carbon phases, the use of
focused/collimated ion beams discloses appealing perspectives for the direct fabrication of
such nanostructures in complex three-dimensional geometries
Micro-beam and pulsed laser beam techniques for the micro-fabrication of diamond surface and bulk structures
Micro-fabrication in diamond is involved in a wide set of emerging
technologies, exploiting the exceptional characteristics of diamond for
application in bio-physics, photonics, radiation detection. Micro ion-beam
irradiation and pulsed laser irradiation are complementary techniques, which
permit the implementation of complex geometries, by modification and
functionalization of surface and/or bulk material, modifying the optical,
electrical and mechanical characteristics of the material. In this article we
summarize the work done in Florence (Italy) concerning ion beam and pulsed
laser beam micro-fabrication in diamond.Comment: 14 pages, 5 figure
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