1,721,027 research outputs found
Some Remarks on the Excitation Threshold of Parametric Rolling in Non-Linear Modelling
No full textIt is known that the parametric excited rolling in following seas can lead to dramatic roll amplitudes and eventually capsizing. On the other hand, the parametric rolling in head waves is a less studied phenomenon: in this case, relative ship velocity is high and consequently the roll damping increases for the effect of forward speed. In this paper, the phenomenon of parametric rolling has been investigated from a mathematical point of view. The KBM perturbation technique has been applied to the nonlinear Mathieu equation describing parametric rolling. The advantages of analytical solutions via perturbation techniques are: “easy” determination of amplitudes of periodic motion and possibility to study the threshold for the onset of parametric rolling with respect to some coefficients. It has been shown that numerical simulation and analytical investigation of simplified equation of motion provide solutions that are in good agreement with model testing
Experimental Investigation of the Bending Vibrations of a Fast Vessels
No full textNowadays, the larger flexibility of ship structures, as well as wave-load spectra shifted to higher frequencies due to high-speed operating regimes, allow the onset of significant vibration phenomena. Recently, there has been increasing interest in combining seakeeping with vibration tests that may result in a deeper physical insight into this topic. In fact, experimental investigations on physical scaled models may benefit general purpose techniques for structural dynamic analysis in order to provide an interesting point of view of the hull vibration problem. The application of methods for modal identification, such as the Output-Only techniques, fi ts the present identification problem, particularly, where the main source of excitation for the structure is the ambient excitation due to the sea waves.
In this paper, the tests carried out in a towing tank basin with an elastically scaled and segmented model are analysed in order to investigate the bending response, ie. bending vibrations modes (shape, frequency and damping) and whipping oscillations. The modal parameters of the "dry" and "wet" modes of the elastic segmented model are identified with the Output-Only technique, based on the Frequency Domain Decomposition. Then, the ship response is analysed in terms of response amplitude operators and recorded time-histories. The correspondence with the full-scale ship, and the dependence of the aforementioned estimations with respect to the forward speed, are highlighted in the paper
Some Remarks on the Nonlinear Modelling of Parametric Rolling
No full textThe stability of upright ship position in longitudinal waves against the onset of parametric rolling has been investigated by a number of authors. The main aim was the analysis of threshold for parametric roll excitation in terms of wave height, ship stability and course. Some researchers investigated also the problem connected with the definition of the threshold in a stochastic environment, but the problem is still partly open. In this paper some shortcomings connected with the linear approach are highlighted, together with a preliminary analysis of the possibility of a nonlinear description based on concentrated parameters nonlinear description of the roll motion amplitude above threshold, a feature that can only be approached taking into account model nonlinearities
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Neuroprotective Effects of Myrtle Berry By-Product Extracts on 6-OHDA-Induced Cytotoxicity in PC12 Cells
Full text linkThe rising global focus on healthy lifestyles and environmental sustainability has prompted interest in repurposing plant-based by-products for health benefits. With increasing life expectancy, the incidence of neurodegenerative diseases-characterized by complex, multifactorial mechanisms such as abnormal protein aggregation, mitochondrial dysfunction, oxidative stress, and inflammation-continues to grow. Medicinal plants, with their diverse bioactive compounds, offer promising therapeutic avenues for such conditions. Myrtus communis L., a Mediterranean plant primarily used in liquor production, generates significant waste rich in antioxidant and anti-inflammatory properties. This study explores the neuroprotective potential of Myrtus berry by-products in a cellular model of neurodegeneration. Using PC12 cells exposed to 6-hydroxydopamine (6-OHDA), we assessed cell viability via MTT assay and measured reactive oxygen species (ROS) production using DCFDA fluorescence. Additionally, we analyzed the expression of genes linked to oxidative stress and neuronal function, including AChE, PON2, Grin1, Gabrd, and c-fos, by RT-PCR. Our findings reveal that Myrtus extract significantly protects against 6-OHDA-induced cytotoxicity, reduces ROS levels, and modulates the expression of key stress-related genes, underscoring its potential as a neuroprotective agent. These results highlight the therapeutic promise of Myrtus extracts in mitigating neurodegenerative processes, paving the way for future interventions
Experimental investigation vs numerical simulation of the dynamic response of a moored floating structure to waves
Full text linkA combined experimental/numerical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used for ships and submarines in special docking operations. The dynamic wave response is investigated by performing experiments in a towing tank equipped with a wave maker. Experimental results are compared with numerical simulations in regular and irregular waves, showing a good agreement. The predicted time histories of pitch, heave and surge motions of the three-body structure and of the mooring line forces bear very satisfactorily the experimental results in regular head waves. The case of irregular waves is also encouraging, since the statistics of the response is correctly kept up to the fourth-order statistical moments. This confirms that the theoretical model proposed in this paper is a suitable tool to predict the actual behaviour of a complex moored structure at sea
Output-Only Analysis for Modal Parameters Estimation of an Elastically Scaled Ship
No full textThe study of the ship structural response assumes an increasing importance as soon as the structures, characterized by much more lightness, are designed and built for faster vessels. This requisite implies a greater flexibility of the structures themselves, the elastic response of which has to be evaluated with accuracy in order to predict the dynamic behavior. In the present paper, a methodology for the identification of the modal parameters from the measurement of only the responses of a vibrating structure has been developed and applied to an elastically scaled model. This output-only technique is successfully applied to the segmented model of a real ship towed in the INSEAN linear basin. The broadband random excitation, provided by the loads exerted by an irregular sea pattern, induces a stochastic response of the model, which is monitored with accelerometers. The obtained results not only outline the parametric dependence of the modal properties on the ship speed, but also suggest a possible practical application of this technique for on-board structural monitoring and fatigue-life prediction
A General and NLP-based Architecture to perform Recommendation: A Use Case for Online Job Search and Skills Acquisition
No full textNatural Language Processing (NLP) is crucial to perform recommendations of items that can be only described by natural language. However, NLP usage within recommendation modules is difficult and usually requires a relevant initial effort, thus limiting its widespread adoption. To overcome this limitation, we introduce FORESEE, a novel architecture that can be instantiated with NLP and Machine Learning (ML) modules to perform recommendations of items that are described by natural language features. Furthermore, we describe an instantiation of such architecture to provide a service for the job market where applicants can verify whether their curriculum vitae (CV) is eligible for a given job position, can receive suggestions about which skills and abilities they should obtain, and finally, can obtain recommendations about online resources which might strengthen their CVs
A Novel Knowledge Plug-In for Incorporating Information About Employability From the O*NET Database Into Conversational Agents
No full textThe labor market is a dynamic and rapidly evolving environment. Job positions that require expertise in various sectors often lead candidates to question their suitability. Therefore, it is crucial to furnish them with relevant, accurate, and timely information. In this article, we introduce a knowledge plug-in for existing conversational agents designed to address specific queries related to the job market domain. Additionally, we propose an innovative method for dynamically creating diverse grammars and semantically associating users' questions with a predefined list of domain questions. We present a novel scheme to effectively tackle question-answering tasks in settings with limited resources. Our architecture relies on question-understanding and response-generation modules, both powered by Transformers, the O*NET occupational database, and recommendation engines that suggest training materials. Furthermore, we conducted a user study based on the System Usability Scale (SUS) score, revealing that users highly appreciated the proposed tool. This sentiment was particularly evident when the tool was integrated with other artificial intelligence chatbots capable of handling general information. Simultaneously, our engine adeptly manages information within the investigated domain, providing precise responses and recommendations. This work addresses a critical gap in the delivery of employment information and paves the way for the development of diverse functionalities to assist both candidates and employers
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