Natural Frequencies of Triple-Walled Carbon Nanotubes

none3noIn this paper, the linear vibrations of Triple-Walled Carbon Nanotubes (TWNTs) are analysed. A multiple elastic shell model is considered. The shell dynamics is studied in the framework of the Sanders-Koiter shell theory. The van der Waals (vdW) interaction between two layers of the TWNT is modelled by a radius-dependent function. The circular cylindrical shell deformation is described in terms of longitudinal, circumferential and radial displacements. Simply supported, clamped and free boundary conditions are considered. The three displacement fields are expanded by means of a double mixed series based on Chebyshev orthogonal polynomials for the longitudinal variable and harmonic functions for the circumferential variable. The Rayleigh-Ritz method is applied to obtain approximate natural frequencies and mode shapes. The present model is validated in linear field by means of data derived from the literature. This study is focused on determining the effect of the geometry and boundary conditions on the natural frequencies of TWNTs.openAndrisano, Angelo O.; Pellicano, Francesco; Strozzi, MatteoAndrisano, Angelo O.; Pellicano, Francesco; Strozzi, Matte

A Testbed About Priority-Based Dynamic Connection Profiles in QoS Wireless Multimedia Networks

The ever-growing demand of high-quality broadband connectivity in mobile scenarios, as well as the Digital Divide discrimination, are boosting the development of more and more efficient wireless technologies. Despite their adaptability and relative small installation costs, wireless networks still lack a full bandwidth availability and are also subject to interference problems. In context of a Metropolitan Area Network serving a large number of users, a bandwidth increase can turn out to be neither feasible nor justified. In consequence, and in order to meet the needs of multimedia applications, bandwidth optimization techniques were designed and developed, such as Traffic Shaping, Policy-Based Traffic Management and Quality of Service (QoS). In this paper, QoS protocols are adopted and, in particular, priority-based dynamic profiles in a QoS wireless multimedia network. This technique allows to asssign different priorities to distinct applications, so as to rearrange service quality in a dynamic way and guarantee the desired performance to a given data flow

How Equalization Techniques Affect the TCP Performance of MC-CDMA Systems in Correlated Fading Channels

This paper investigates the impact of several equalization techniques for multicarrier code division multiple access systems on the performance at both lower and upper layers (i.e., physical and TCP layers). Classical techniques such as maximal ratio combining, equal gain combining, orthogonality restoring combining, minimum mean square error, as well as a partial equalization (PE) are investigated in time- and frequency-correlated fading channels with various numbers of interferers. Their impact on the performance at upper level is then studied. The results are obtained through an integrated simulation platform carefully reproducing all main aspects affecting the quality of service perceived by the final user, allowing an investigation of the real gain produced by signal processing techniques at TCP level

Prototipazione virtuale e simulazione di un mandrino cedevole per la sbavatura robotizzata

Allo stato dell\u2019arte corrente, la Sbavatura Robotizzata (SR) \ue8 stata adottata con successo in numerose applicazioni industriali, ma richiede ancora miglioramenti in termini di qualit\ue0 finale. Infatti, l\u2019efficacia di un processo di SR \ue8 altamente influenzata dalla limitata precisione dei movimenti del robot e dalle imprevedibili variazioni di dimensioni e forma delle bave. La cedevolezza dell\u2019utensile risolve parzialmente il problema, nonostante si rendano necessari strumenti dedicati di \u201cengineering design\u201d, allo scopo di identificare quei parametri ottimizzati e quelle strategie di SR che consentano di ottenere la miglior qualit\ue0 e il miglior rapporto costo-efficacia. In questo contesto, il presente lavoro propone un Prototipo Virtuale (PV) di un mandrino pneumatico dotato di cedevolezza intrinseca, adatto a valutare l\u2019efficienza del processo in diversi scenari. Il PV proposto \ue8 stato creato integrando un modello multi-body della struttura meccanica del mandrino con un modello matematico delle forze di processo. Vengono infine illustrate simulazioni numeriche, atte a prevedere sia le forze di taglio che l\u2019accuratezza della finitura superficiale

Monoterpene indole alkaloids from Vinca minor L. (Apocynaceae): Identification of new structural scaffold for treatment of Alzheimer's disease

One undescribed indole alkaloid together with twenty-two known compounds have been isolated from aerial parts of Vinca minor L. (Apocynaceae). The chemical structures of the isolated alkaloids were determined by a combination of MS, HRMS, 1D, and 2D NMR techniques, and by comparison with literature data. The NMR data of several alkaloids have been revised, corrected, and missing data have been supplemented. Alkaloids isolated in sufficient quantity were screened for their in vitro acetylcholinesterase (AChE; E.C. 3.1.1.7) and butyrylcholinesterase (BuChE; E.C. 3.1.1.8) inhibitory activity. Selected compounds were also evaluated for prolyl oligopeptidase (POP; E.C. 3.4.21.26), and glycogen synthase 3β-kinase (GSK-3β; E.C. 2.7.11.26) inhibition potential. Significant hBuChE inhibition activity has been shown by (−)-2-ethyl-3[2-(3-ethylpiperidinyl)-ethyl]-1H-indole with an IC50 value of 0.65 ± 0.16 μM. This compound was further studied by enzyme kinetics, along with in silico techniques, to reveal the mode of inhibition. This compound is also predicted to cross the blood-brain barrier (BBB) through passive diffusion

School-based prevention for adolescent Internet addiction: prevention is the key. A systematic literature review

Adolescents’ media use represents a normative need for information, communication, recreation and functionality, yet problematic Internet use has increased. Given the arguably alarming prevalence rates worldwide and the increasingly problematic use of gaming and social media, the need for an integration of prevention efforts appears to be timely. The aim of this systematic literature review is (i) to identify school-based prevention programmes or protocols for Internet Addiction targeting adolescents within the school context and to examine the programmes’ effectiveness, and (ii) to highlight strengths, limitations, and best practices to inform the design of new initiatives, by capitalizing on these studies’ recommendations. The findings of the reviewed studies to date presented mixed outcomes and are in need of further empirical evidence. The current review identified the following needs to be addressed in future designs to: (i) define the clinical status of Internet Addiction more precisely, (ii) use more current psychometrically robust assessment tools for the measurement of effectiveness (based on the most recent empirical developments), (iii) reconsider the main outcome of Internet time reduction as it appears to be problematic, (iv) build methodologically sound evidence-based prevention programmes, (v) focus on skill enhancement and the use of protective and harm-reducing factors, and (vi) include IA as one of the risk behaviours in multi-risk behaviour interventions. These appear to be crucial factors in addressing future research designs and the formulation of new prevention initiatives. Validated findings could then inform promising strategies for IA and gaming prevention in public policy and education