Nonlinear Resonance Interaction between Conjugate Circumferential Flexural Modes in Single-Walled Carbon Nanotubes

This paper presents an investigation on the dynamical properties of single-walled carbon nanotubes (SWCNTs), and nonlinear modal interaction and energy exchange are analysed in detail. Resonance interactions between two conjugate circumferential flexural modes (CFMs) are investigated. The nanotubes are analysed through a continuous shell model, and a thin shell theory is used to model the dynamics of the system; free-free boundary conditions are considered. The Rayleigh-Ritz method is applied to approximate linear eigenfunctions of the partial differential equations that govern the shell dynamics. An energy approach, based on Lagrange equations and series expansion of the displacements, is considered to reduce the initial partial differential equations to a set of nonlinear ordinary differential equations of motion. The model is validated in linear field (natural frequencies) by means of comparisons with literature. A convergence analysis is carried out in order to obtain the smallest modal expansion able to simulate the nonlinear regimes. The time evolution of the nonlinear energy distribution over the SWCNT surface is studied. The nonlinear dynamics of the system is analysed by means of phase portraits. The resonance interaction and energy transfer between the conjugate CFMs are investigated. A travelling wave moving along the circumferential direction of the SWCNT is observed

Novel spectral kurtosis technology for adaptive vibration condition monitoring of multi-stage gearboxes

In this paper, the novel wavelet spectral kurtosis (WSK) technique is applied for the early diagnosis of gear tooth faults. Two variants of the wavelet spectral kurtosis technique, called variable resolution WSK and constant resolution WSK, are considered for the diagnosis of pitting gear faults. The gear residual signal, obtained by filtering the gear mesh frequencies, is used as the input to the SK algorithm. The advantages of using the wavelet-based SK techniques when compared to classical Fourier transform (FT)-based SK is confirmed by estimating the toothwise Fisher's criterion of diagnostic features. The final diagnosis decision is made by a three-stage decision-making technique based on the weighted majority rule. The probability of the correct diagnosis is estimated for each SK technique for comparison. An experimental study is presented in detail to test the performance of the wavelet spectral kurtosis techniques and the decision-making technique

Asymmetric vibrations and chaos in spherical caps under uniform time-varying pressure fields

This paper presents a study on nonlinear asymmetric vibrations in shallow spherical caps under pressure loading. The Novozhilov’s nonlinear shell theory is used for modeling the structural strains. A reduced-order model is developed through the Rayleigh–Ritz method and Lagrange equations. The equations of motion are numerically integrated using an implicit solver. The bifurcation scenario is addressed by varying the external excitation frequency. The occurrence of asymmetric vibrations related to quasiperiodic and chaotic motion is shown through the analysis of time histories, spectra, Poincaré maps, and phase planes

Nonlinear vibration of continuous systems

Continuous systems, such as beams, membranes, plates, shells, and other structural/mechanical components, represent fundamental elements of mechanical systems in any field of engineering: Aerospace, Aeronautics, Automation, Automotive, Civil, Nuclear, Petroleum, and Railways. The modern designer is required to optimize structural elements to improve the performance-to-cost ratio, produce lightweight machines, and improve the efficiency. Such optimizations easily lead to a magnification of vibration/dynamic problems such as resonances, instabilities, and nonlinear behaviors. Therefore, the development of new methods of analysis, testing, and monitoring is greatly welcome. This special issue focuses on sharing recent advances and developments of theories, algorithms, and applications that involve the dynamics and vibrations of continuous systems. The contributions to this special issue include innovative theoretical studies, advanced numerical simulations, and new experimental approaches to investigate and better understand complex dynamic phenomena; more specifically, methods and theories for beams, membranes, plates, and shells; numerical approaches for structural elements; fluid-structure interaction; nonlinear acoustics; identification, diagnosis, friction models, and vehicle dynamics. Seventeen contributions have been received from all over the world: Canada, China, Kazakhstan, Italy, Macau, Spain, and USA. This shows the generalized interest on the topic. The following short description of the special issue content is organized by grouping the contributions in coherent subtopics

Resonances and nonlinear vibrations of circular cylindrical shells, effects of thermal gradients

In this paper, the results of an experimental campaign focused on the vibrations of shells are presented. More specifically, the goal is to investigate the effect of thermal gradients across the shell thickness on the nonlinear dynamics. The shell is made of polymeric material and an aluminum mass is clamped on one end of the shell; the other shell end is clamped to an electrodynamic shaker, which provides a base harmonic excitation. Tests are performed in a controlled environment where a thermal gradient on the shell thickness is generated by means of a climatic chamber and an internal cartridge heater. Different temperature gradients and base excitation levels have been considered. The nonlinear dynamic scenario is analyzed through amplitude–frequency diagrams, bifurcation diagrams, waterfall diagrams, time histories, Fourier spectra, phase portraits, and Poincaré maps. Results show a strong effect of the temperature on the dynamic response of the shell: subharmonic, quasi-periodic, and chaotic vibrations take place as well as large amplitude vibrations, high sound levels are detected

Employability skills: Profiling data scientists in the digital labour market

In the current scenario, data scientists are expected to make sense of vast stores of big data, which are becoming increasingly complex and heterogeneous in nature. In the context of today's rapid technological development and its application in a growing array of fields, this role is evolving simultaneously. The present study provides an insight into the current expectations of employers seeking to hire individuals with this job title. It is argued that gaining a better understanding of data scientists’ employability criteria and the evolution of this professional role is crucial. The focus is placed on the desired prerequisites articulated through job advertisements, thus deriving relevant means for furthering theory and practice. It was achieved by harvesting relevant data from job advertisements published on US employment websites, which currently attract the US market's highest recruitment traffic. The key contribution of this study is to have identified means of systematically mapping skills, experience, and qualifications sought by employers for their data scientists, thus providing a data-driven pathway for employability and avoiding skills gaps and mismatches in a profession that is pivotal in the Industry 4.0

Regulation of cell proliferation and apoptosis in neuroblastoma cells by ccp1, a FGF2 downstream gene

Background: Coiled-coil domain containing 115 (Ccdc115) or coiled coil protein-1 (ccp1) was previously identified as a downstream gene of Fibroblast Growth Factor 2 (FGF2) highly expressed in embryonic and adult brain. However, its function has not been characterised to date. Here we hypothesized that ccp1 may be a downstream effecter of FGF2, promoting cell proliferation and protecting from apoptosis. Methods: Forced ccp1 expression in mouse embryonic fibroblast (MEF) and neuroblastoma SK-N-SH cell line, as well as down-regulation of ccp1 expression by siRNA in NIH3T3, was used to characterize the role of ccp1. Results: Ccp1 over-expression increased cell proliferation, whereas down-regulation of ccp1 expression reduced it. Ccp1 was able to increase cell proliferation in the absence of serum. Furthermore, ccp1 reduced apoptosis upon withdrawal of serum in SK-N-SH. The mitogen-activated protein kinase (MAPK) or ERK Kinase (MEK) inhibitor, U0126, only partially inhibited the ccp1-dependent BrdU incorporation, indicating that other signaling pathway may be involved in ccp1-induced cell proliferation. Induction of Sprouty (SPRY) upon FGF2 treatment was accelerated in ccp1 over-expressing cells. Conclusions: All together, the results showed that ccp1 regulates cell number by promoting proliferation and suppressing cell death. FGF2 was shown to enhance the effects of ccp1, however, it is likely that other mitogenic factors present in the serum can also enhance the effects. Whether these effects are mediated by FGF2 influencing the ccp1 function or by increasing the ccp1 expression level is still unclear. At least some of the proliferative regulation by ccp1 is mediated by MAPK, however other signaling pathways are likely to be involved

Psychiatric profile of motor subtypes of de novo drug-naïve Parkinson's disease patients

Background: Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder. It is well established that different motor subtypes of PD evolve with different clinical courses and prognoses. The complete psychiatric profile underlying these different phenotypes since the very early stage of the disease is debated. Aims of the study: We aimed at investigating the psychiatric profile of the three motor subtypes of PD (akinetic-rigid, tremor-dominant, and mixed) in de novo drug-naïve patients with PD. Methods: Sixty-eight patients with PD, divided into 39 akinetic-rigid (AR), seven mixed (MIX), and 22 tremor-dominant (TD) patients underwent a complete assessment of psychiatric, cognitive, and motor symptoms. Results: No significant differences were found among groups. Conclusions: Our results suggest that a differentiation of the psychiatric symptoms associated with specific motor subtypes of PD is not detectable in de novo drug-naïve patients. Previous evidence that emerges later along the disease progression may be a consequence of the dopaminergic and nondopaminergic damage increase