86,705 research outputs found
Degenerate integrodifferential equations of Volterra type in Banach space
No full textIl contributo è un articolo scientifico originale, non pubblicato altrove in nessuna forma.
Introduction: "This paper is concerned with the following degenerate integro-differential equation of parabolic type: \gathered \frac{d}{dt}(M(t)u(t))+L(t)u(t)+\int_0^t K(t,s)u(s)ds=f(t),\\0\leq t\leq T, M(t)u(t)|_{t=0}=M(0)u_0.\endgathered\tag1 This type of equation without the integral terms is discussed in great detail in Chapters III and IV of the book \ref[A. Favini and A. Yagi, Degenerate differential equations in Banach spaces, Dekker, New York, 1999; MR1654663 (99i:34079)] based on the theory of analytic semigroups generated by multi-valued linear operators. In Section 1, making intensive use of the results of [op. cit. (Chapter IV)], we show the existence and uniqueness of a solution to the non-autonomous equation (1) described above. We use the idea of M. G. Crandall and J. A. Nohel \ref[Israel J. Math. 29 (1978), no. 4, 313--328; MR0477910 (57 \#17410) (Proposition 1)] to deal with the integral term. Section 2 is devoted to the autonomous case based on the results of Chapter III of [A. Favini and A. Yagi, op. cit.]. In the non-autonomous case rather restrictive assumptions are required for certain constants which appear in the hypothesis for the operators and . In the autonomous case this restriction is considerably relaxed. Finally in Section 3 we consider the case in which the assumption (P) of [A. Favini and A. Yagi, op. cit. (p. 92)] is satisfied with . In this case using the method of J. Prüss \ref[J. Integral Equations 5 (1983), no. 3, 211--236; MR0702432 (85d:45026)], we show the existence and uniqueness of a function satisfying the integro-differential equation (1) with the integral term understood in the improper sense under a weaker assumption on the initial data.
Pressure Oscillations Numerical Simulation In Solid Rocket Motors
No full textLarge solid rocket motors can be affected by sustained pressure and thrust oscillations during the quasi-steady state. The root cause of this phenomenon is represented by the coupling between the vortices generation, shedding, advection and interaction with the SRM chamber geometry and the acoustic chamber modes excitement, which may act together, in a feedback coupled loop. In the present work, a Q1D model for the simulation of the pressure oscillations in solid rocket motors, named AGAR (Aerodynamically Generated Acoustic Resonance), is described, discussing a new formulation of the Q1D vorticity equation and of the closure terms for modeling the vortex sound generation. The results of the pressure oscillations simulation yielded with the new model formulation are discussed for the P80 solid rocket motor, first stage of the European launcher VEGA. © 2012 by E. Cavallini, V. Ferretti, B. Favini, M. Di Giacinto, F. Serraglia
Analysis of VEGA solid stages static firing tests towards the maiden flight
No full textVEGA is the new launcher developed by the European Space Agency and qualified with its maiden flight on February, 13rd 2012. During the launcher development, a total of eight static firing tests have been performed for the three solid stages (VEGA family SRMs), which compose the launcher: the first stage P80, the second stage Zefiro 23 and the third stage Z9A. In this work, the analysis of the static firing tests of the VEGA SRMs is performed with a post-static firing test reconstruction model, developed for the purpose. The aim is to use the measures acquired during the SFTs, in order to evaluate the actual behavior of the SRMs, through the parameters: combustion efficiency, thrust efficiency, hump, scale factor and nozzle throat area law, which define the actual performance parameters of the SRMs. The final purpose is to assess the SRMs performance parameters from the SFT data; to investigate the actual internal ballistics of the SRMs, comparing the outcomes of the SFT analysis, for each stage and, all together, all the VEGA family SRMs, in order to make possible the extrapolation of the flight conditions and to analyze the VEGA maiden flight. © 2012 by E. Cavallini, B. Favini, M. Di Giacinto, F. Serraglia
Propellant effects on SRM upper stage internal ballistics and performance with nozzle erosion characterization
No full textNozzle throat erosion is inherently present in high performance solid rocket motors because of high operative pressures and long combustion times. Whereas for large SRM boosters, operating in atmosphere, it does not represent a strong limit to obtain high performance, for upper stage SRMs it brings to relevant losses in the specific impulse and, hence, less effcient design of the solid rocket motor due to the nozzle throat erosion effects on both the operative pressure and specific impulse. This paper discusses the effects on the performance of an upper stage SRM of different kinds of aluminized propellants, compared to the baseline propellant HTPB 1912. The reference configuration is Zefiro 9A, third stage of the European launcher VEGA, recently qualified with its first maiden flight. The analysis is performed with the use of the complete coupling of the following models: a 3D grain burnback model, GREG, a full Navier-Stokes simulation of the nozzle throat erosion and a Q1D model of the SRM internal ballistic. © 2012 by E. Cavallini, D. Bianchi, B. Favini, M. Di Giacinto, F. Serraglia
School-Based Interventions to Reduce Internet-related Addictions in Youths: Preliminary Findings from an Italian Pilot Study
No full textIntroduction: During the last years, internet-related problematic and addictive behaviors gained increasing attention, due to their effects on mental health, especially in youths, which show the highest vulnerability to these problems, given their high frequency of ICT use and digital literacy (Andreassen et al., 2017; Cheng et al., 2021).
Nowadays Internet and Information and Communication Technologies (ICT) become core instruments of everyone’s daily lives, for carrying out academic, work, relational, or entertainment activities (Oka et al., 2021). Taking this in mind is fundamental in
distinguishing between positive and problematic use (e.g., Gjoneska et al., 2022). Positive ICT use motivates people to interact directly with others and is positively associated with
well-being, while massive and negative ICT use increases maladjustment, such as emotional problems, behavioral problems, or work-related and academic problems (e.g., Alimoradi et
al., 2019; Oka et al., 2021).
To prevent internet-related addictive behaviors, and to promote positive ICT use, a school-based intervention was carried out over the last school year in Rome (Italy). Four meetings were conducted with students, and each meeting conceived an educational session followed by practical experiences.
Aims of this study: The study aimed to preliminary investigate the effectiveness of the intervention, by analyzing mean differences of two negative and two positive internet-related behaviors in youths.
Method and Results: 358 youths (35% females; Mage=15.35, S.D.=.63) completed the Bergen Social Media Addiction Scale (Monacis et al., 2017), the Smartphone Addiction Scale (Kwon
et al., 2013), and the Active and Passive Use of Social Networking Sites Scale (Remondi et al., 2022) in the pre-and-post intervention assessments (Npre-int=375; Npost-int=258). Repeated Analysis of Variances showed that smartphone and SN addictions significantly decreased from pre-to-post assessments (i.e., F [1,229] = 7.95; p = .005; eta-square = .03; F [1,230] = 5.56; p = .01; eta-square = .02). In addition, offering and searching social support on SN significantly increased from pre-to-post assessments (i.e., F [1,233] = 5.07; p = .02; eta-square = .02; F [1,230] = 5.60; p = .02; eta-square = .02).
Discussion: Our findings showed that problematic smartphone and SN use significantly decreased, while relational activities engaged with SN significantly increased across the intervention. These results suggested the short-term efficacy of the project and could be considered in the implementation of other school-based interventions, and in the implementation of more effective socioeconomic strategies to contrast internet-related addictive behaviors (Andreassen et al., 2017)
Modeling of Flowfield Features During Ignition Transient of Solid Rocket Motor
No full textAIAA Paper 2002-375
Analysis & reconstruction of pressure oscillations during P80 steady-state of VEGA flights
No full textPressure oscillations can characterize the steady phase of large solid rocket motors, entailing dynamic loads on the launch vehicle structure and thrust oscillations. Both the modern large lower stage/booster configurations, segmented SRMs - e.g. Ariane 5 and Space Shuttle boosters - and monolithic finocyl SRMs - e.g. P80 of VEGA, are prone to pressure oscillations phenomena, at frequencies of the firsts longitudinal modes of the combustion chamber, with different characteristics time windows: during the second half of the SRM functioning, for the segmented SRMs; during the first half of the operative life, for the aft-finocyl configurations. This study is aimed at presenting the analysis of pressure oscillations of a real aft-finocyl SRM, addressing the following points: discuss and analyse the signature with the associated dispersion of the pressure oscillations phenomena (both in time and frequency domain) of the aft-finocyl first stage of the European launch vehicle VEGA, P80 SRM, exploiting the flight data from the first six flights over the nine successfully flown to date; provide a reconstruction and analysis of the pressure oscillation phenomena of the P80 SRM with the use of a Q1D aero-acoustic model of pressure oscillations in aft-finocyl SRMs, named AGAR, showing the capability of the model to represent with good correlation the whole experimental signature of the pressure oscillations experienced by P80 SRM during the flights
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