Theory of Reciprocating Contact for Viscoelastic Solids

A theory of reciprocating contacts for linear viscoelastic materials is presented. Results are discussed for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. Depending on the size of the contact, the frequency and amplitude of the reciprocating motion, and on the relaxation time of the viscoelastic body, we establish that the contact behavior may range from the steady-state viscoelastic solution, in which traction forces always oppose the direction of the sliding rigid punch, to a more elaborate trend, never observed before, which is due to the strong interaction between different regions of the path covered during the reciprocating motion. Practical implications span a number of applications, ranging from seismic engineering to biotechnology.Comment: 8 pages, 5 figures, accepted for publication on Physical Review E, March 22, 201

A Comprehensive Atlas of Perineuronal Net Distribution and Colocalization with Parvalbumin in the Adult Mouse Brain

Perineuronal nets (PNNs) surround specific neurons in the brain and are involved in various forms of plasticity and clinical conditions. However, our understanding of the PNN role in these phenomena is limited by the lack of highly quantitative maps of PNN distribution and association with specific cell types. Here, we present a comprehensive atlas of Wisteria Floribunda Agglutinin (WFA) positive PNNs and colocalization with parvalbumin (PV) cells for over 600 regions of the adult mouse brain. Data analysis shows that PV expression is a good predictor of PNN aggregation. In the cortex, PNNs are dramatically enriched in layer 4 of all primary sensory areas in correlation with thalamocortical input density, and their distribution mirrors intracortical connectivity patterns. Gene expression analysis identifies many PNN correlated genes. Strikingly, PNN anticorrelated transcripts are enriched in synaptic plasticity genes, generalizing PNN role as circuit stability factors

mGluR5 PAMs rescue cortical and behavioural defects in a mouse model of CDKL5 deficiency disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a devastating rare neurodevelopmental disease without a cure, caused by mutations of the serine/threonine kinase CDKL5 highly expressed in the forebrain. CDD is characterized by early-onset seizures, severe intellectual disabilities, autistic-like traits, sensorimotor and cortical visual impairments (CVI). The lack of an effective therapeutic strategy for CDD urgently demands the identification of novel druggable targets potentially relevant for CDD pathophysiology. To this aim, we studied Class I metabotropic glutamate receptors 5 (mGluR5) because of their important role in the neuropathological signs produced by the lack of CDKL5 in-vivo, such as defective synaptogenesis, dendritic spines formation/maturation, synaptic transmission and plasticity. Importantly, mGluR5 function strictly depends on the correct expression of the postsynaptic protein Homer1bc that we previously found atypical in the cerebral cortex of Cdkl5-/y mice. In this study, we reveal that CDKL5 loss tampers with (i) the binding strength of Homer1bc-mGluR5 complexes, (ii) the synaptic localization of mGluR5 and (iii) the mGluR5-mediated enhancement of NMDA-induced neuronal responses. Importantly, we showed that the stimulation of mGluR5 activity by administering in mice specific positive-allosteric-modulators (PAMs), i.e., 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) or RO6807794, corrected the synaptic, functional and behavioral defects shown by Cdkl5-/y mice. Notably, in the visual cortex of 2 CDD patients we found changes in synaptic organization that recapitulate those of mutant CDKL5 mice, including the reduced expression of mGluR5, suggesting that these receptors represent a promising therapeutic target for CDD

Il Market Participants Acquisition Premium e gli adjusted control premia: evidenze empiriche sul mercato europeo

Il lavoro di tesi si apre con la revisione della letteratura sui premi di controllo. Si commentano in particolar modo le critiche alle tradizionali modalità di determinazione degli equity premium. Il secondo capitolo si focalizza sui più importanti premi e sconti utilizzati in valutazione d’azienda, sulle basi e sulle configurazioni di valore. Il terzo capitolo introduce al Market Participant Acquisition Premium e commenta la letteratura sui ripensamenti riguardo i premi di controllo. Il lavoro prosegue con l’analisi delle best practices emanate dall’Appraisal Foundation sulla valutazione dei premi di controllo per il financial reporting. Vengono discusse le rinnovate modalità di determinazione degli acquisition premium e si commentano i fattori che influenzano la loro determinazione. L’ultimo capitolo, il quinto, commenta le risultanze empiriche di uno studio sulle transazioni recentemente conclusesi sul mercato europeo. Viene studiata la relazione tra i premi di acquisizione e diverse variabili caratterizzanti le transazioni. In seguito si riportano due modalità di determinazione degli adjusted control premium. The thesis work opens with a review of the literature on control premium. In particular, this part discuss criticism of traditional methods of determining equity premium . The second chapter focuses on the most important premiums and discounts used in business valuation, and on the standards of value. The third chapter introduces the Market Participant Acquisition Premium and comments rethinkings on control premium known in literature. The work continues with an analysis of best practices issued by the Appraisal Foundation on the valuation of control premiums for financial reporting. The revised methods of determining acquisition premium are discussed and factors that influence their determination are commented. The last chapter, the fifth, comments the empirical findings of a study on recently concluded transactions in the European market. The relationship between acquisition premiums and various variables characterizing transactions is studied. Two methods of determining adjusted control premium are described

Recent Advancements in the Tribological Modelling of Rough Interfaces

This paper analyses some effective strategies proposed in the last few years to tackle contact mechanics problems involving rough interfaces. In particular, we present Boundary Element Methods capable of solving the contact with great accuracy and, at the same time, with a marked computational efficiency. Particular attention is paid to non-linearly elastic constitutive relations and, specifically, to a linearly viscoelastic rheology. Possible implications deal with all the tribological mechanical systems, where contact interactions are present, including, e.g., seals, bearings and dampers

Equilibrium states and stability of pre-tensioned adhesive tapes

In the present paper we propose a generalization of the model developed in Afferrante, L.; Carbone, G.; Demelio, G.; Pugno, N. Tribol. Lett. 2013, 52, 439–447 to take into account the effect of the pre-tension in the tape. A detailed analysis of the peeling process shows the existence of two possible detachment regimes: one being stable and the other being unstable, depending on the initial configuration of the tape. In the stability region, as the peeling process advances, the peeling angle reaches a limiting value, which only depends on the geometry, on the elastic modulus of the tape and on the surface energy of adhesion. Vice versa, in the unstable region, depending on the initial conditions of the system, the tape can evolve towards a state of complete detachment or fail before reaching a state of equilibrium with complete adhesion. We find that the presence of pre-tension in the tape does not modify the stability behavior of the system, but significantly affects the pull-off force which can be sustained by the tape before complete detachment. Moreover, above a critical value of the pre-tension, which depends on the surface energy of adhesion, the tape will tend to spontaneously detach from the substrate. In this case, an external force is necessary to avoid spontaneous detachment and make the tape adhering to the substrate

Friction in rough contacts of linear viscoelastic surfaces with anisotropic statistical properties

Viscoelastic rheology can have great effects on the contact mechanics of randomly rough surfaces with anisotropic statistical properties. In this paper, we investigate such effects in the framework of Persson’s theory. We calculate the forces that arise in viscoelastic contacts because of the viscous dissipation occurring in the bulk material. Interestingly, the non-symmetric distribution of the normal contact pressure entails the occurrence of a force in the direction perpendicular to the sliding one. Such force does not carry out any work, and hence does not dissipate energy, but it is important for the global equilibrium of the system. Results are also compared with numerical exact calculations finding a quite good agreement. However, with the present method, we cannot capture the stretching of the contact clusters due to the viscoelasticity and, hence, the resulting change in the anisotropy of the deformed surface