Analysis of pressure blips in aft-finocyl solid rocket motor

Ballistic anomalies have frequently occurred during the firing of several solid rocket motors (SRMs) (Inertial Upper Stage, Space Shuttle Redesigned SRM (RSRM) and Titan IV SRM Upgrade (SRMU)), producing even relevant and unexpected variations of the SRM pressure trace from its nominal profile. This paper has the purpose to provide a numerical analysis of the following possible causes of ballistic anomalies in SRMs: an inert object discharge, a slag ejection, and an unexpected increase in the propellant burning rate or in the combustion surface. The SRM configuration under investigation is an aft-finocyl SRM with a first-stage/small booster design. The numerical simulations are performed with a quasi-one-dimensional (Q1D) unsteady model of the SRM internal ballistics, properly tailored to model each possible cause of the ballistic anomalies. The results have shown that a classification based on the head-end pressure (HEP) signature, relating each other the HEP shape and the ballistic anomaly cause, can be made. For each cause of ballistic anomalies, a deepened discussion of the parameters driving the HEP signatures is provided, as well as qualitative and quantitative assessments of the resultant pressure signals

Corrosion of bronzes by extended wetting with single versus mixed acidic pollutants

The corrosion of bronzes was examined in the context of single-acid versus mixed-acid (as in urban acid rain) solutions. Two bi-component bronzes (copper with either 3% Sn or 7% Sn) that closely represent those of historic artifacts were immersed for five weeks in conditions designed to replicate those experienced by statues and ornaments in cities where rainfall and humidity constantly produce an electrolyte layer on the surfaces of bronzes. Ions, acids, and particles of pollutants can dissolve in this layer, resulting in a variety of harsh corrosion processes. The kinetics of corrosion and the properties of the resulting patinas were monitored weekly by electrochemical impedance spectroscopy and open-circuit potential measurements. The sizes and appearances of the corrosion products were monitored and used to estimate the progress of the corrosion, whose crystalline structures were visualized using scanning electron microscopy with energy dispersive spectroscopy, identified by X-ray diffraction, and characterized by spectrocolorimetry. The electrochemical measurements demonstrated that greater damage (in terms of color change and corrosion product formation) did not correspond to deficiencies in protection. The mixed-acid solution did not corrode the bronzes, as would be expected from the additive effects of the single acids. The postulated mechanisms of metal dissolution appear to be specific to a particular bronze alloy, with the tin component playing an important role

Wet and dry accelerated aging tests in a spray chamber to understand the effects of acid rain frequencies on bronze corrosion

We have conducted controlled laboratory experiments using a series of bronze alloys exposed to frequent, repeated wet and dry cycles, to simulate frequent acid rain exposure and study the resultant corrosion processes in bronze artifacts exposed to an outdoor urban environment. To simulate rainwater and condensation, a spray chamber for the corrosion tests was assembled, which delivered homogeneous vapor diffusion and drop deposition. Three bi-component bronzes, with 3%, 7% and 20% tin content, were subjected to seven days of controlled wet and dry cycles, and analyzed at precise intervals. Electrochemical impedance spectroscopy and spectrocolorimetry results were combined to show the different phases of corrosion. The patinas on all three samples at the end of the exposure period were studied with scanning electron microscopy to show the morphology of corrosion products; they were also analyzed by X-ray diffraction. The sample containing 7% tin produces a patina that is unstable and frequently dissolved. Partial patina dissolution also occurs during exposure for the 3% tin sample, but the effects are less pronounced. Because it reacts the least with the environment, the 20% tin sample demonstrates intermediate behavior (between the 7% and the 3% tin samples). However, the patina is less protective than the 3% tin sample patina

Instrument and data analysis challenges for imaging spectropolarimetry

The next generation of solar telescopes will enable us to resolve the fundamental scales of the solar atmosphere, i.e., the pressure scale height and the photon mean free path. High-resolution observations of small-scale structures with sizes down to 50 km require complex post-focus instruments, which employ adaptive optics (AO) and benefit from advanced image restoration techniques. The GREGOR Fabry-Perot Interferometer (GFPI) will serve as an example of such an instrument to illustrate the challenges that are to be expected in instrumentation and data analysis with the next generation of solar telescopes.Comment: 4 pages, 1 figure, accepted for publication in Astronomische Nachrichten/AN, special issue of the 1st EAST-ATST Workshop: "Science with large solar telescopes" in Freiburg, Germany, October 14-16, 200

New technique to measure the cavity defects of Fabry-Perot interferometers

(Abridged): We define and test a new technique to accurately measure the cavity defects of air-spaced FPIs, including distortions due to the spectral tuning process typical of astronomical observations. We further develop a correction technique to maintain the shape of the cavity as constant as possible during the spectral scan. These are necessary steps to optimize the spectral transmission profile of a two-dimensional spectrograph using one or more FPIs. We devise a generalization of the techniques developed for the so-called phase-shifting interferometry to the case of FPIs. The technique is applicable to any FPI that can be tuned via changing the cavity spacing ($z$-axis), and can be used for any etalon regardless of the coating' reflectivity. The major strength of our method is the ability to fully characterize the cavity during a spectral scan, allowing for the determination of scan-dependent modifications of the plates. As a test, we have applied this technique to three 50 mm diameter interferometers, with cavity gaps ranging between 600 micron and 3 mm, coated for use in the visible range. We obtain accurate and reliable measures of the cavity defects of air-spaced FPIs, and of their evolution during the entire spectral scan. Our main, and unexpected, result is that the relative tilt between the two FPI plates varies significantly during the spectral scan, and can dominate the cavity defects; in particular, we observe that the tilt component at the extremes of the scan is sensibly larger than at the center of the scan. Exploiting the capability of the electronic controllers to set the reference plane at any given spectral step, we develop a correction technique that allows the minimization of the tilt during a complete spectral scan. The correction remains highly stable over long periods, well beyond the typical duration of astronomical observations.Comment: 15 pages, 20+ figures, accepted for publication in A&A. Two additional movies are available in the online version of the pape

Folk and Popular as "National": The Invention of the Italian Unity through Poetry and Music

La nascita delle moderne filologia, musicologia ed etnologia nel XIX sec. ha contribuito ad approfondire anche in Italia lo studio scientifico della poesia e della musica non cólte. I termini popolare e nazionale, tuttavia, erano passibili all’epoca delle interpretazioni più varie, in virtù del diverso approccio delle tre discipline alla materia. Gli storici della letteratura si occupavano infatti di poesia con scarsa sensibilità per la musica, i musicologi di musica antica senza alcuna preparazione letteraria, gli etnologi indagavano i fenomeni nel loro accadere e solo in qualche caso formulavano ipotesi sulla storicità delle tradizioni. La prima generazione di studiosi delle tre branche postulava inoltre l’unità linguistica del paese, come dimostra la teoria monogenetica del tetrastico da cui si è generato lo strambotto, secondo la quale i dialetti sarebbero varianti dello stesso nucleo sorto in Sicilia e migrato in Toscana, come accadde per la poesia colta secondo l’opinione di Carducci. Tesi duplicata da Nigra con l’origine celtica della canzone e sicula dello strambotto, fondata sul pregiudizio della diversa indole razziale delle genti del Nord e del Sud, che non nega però la comune origine latina dei due ceppi. L’identificazione del popolo creatore collocato in via esclusiva nel passato e le dialettiche di trasmissione dei canti hanno occupato il dibattito in relazione alla musica, guardata come il medium privilegiato per la veicolazione del testo popolare. I musicologi, dal canto loro, non hanno mai usato il concetto di classe e si sono limitati a descrivere come popolare una parte dell’antica polifonia profana. Il trend si è radicalizzato sul finire dell’Ottocento, a causa della reazione nazionalista che agì negativamente anche sulla filologia. Basti pensare ai “cantari leggendari” forzatamente assimilati all’epica romanza e germanica. In questo caso il popolo che canta è facilmente omologabile al concetto di nazione, cui si richiamavano in musica i vari Torchi, Parodi, Silva e Tommasini. Non stupisce quindi l’accoglimento della “filologia delle origini” da parte di Favara, il quale, come d’Annunzio, era affascinato dalla melodia primordiale e dagli archetipi del popolare. Laddove il popolare coincide con la musica e il dialetto, in cui si riconosce il perenne dionisiaco separato dall’apollineo al quale si piega la lingua. Le due categorie metastoriche hanno consentito così di superare l’impasse di un bilinguismo culturale che avrebbe reso inconciliabili lo studio del canto folklorico e la filosofia di Nietzsche, poiché lo studioso non attendeva alla ricerca in senso diacronico, ma alla registrazione nell’ hic et nunc di fenomeni che nei modi si ripetono sempre eguali nel tempo. Per cui la settorializzazione dei saperi, invece di aprire una fenditura nei processi di classificazione regolati su dinamiche di creazione-ricezione dal basso all’alto e viceversa, favorì l’occultamento del concetto di classe e delle relative stratificazioni culturali multiple.Before and after the territorial unity of Italy in 1861, some scholars concentrated all their efforts on unifying the language and the culture of the country, without taking into consideration both the regional inner division and the dialects. The investigation on the studies about vernacular poetry accompanied by music testifies that there was a passage from a research phase based on the regional songs to a phase devoted to the general survey of the new state. For instance Costantino Nigra (La poesia popolare italiana, 1876) and Alessandro D’Ancona (La poesia popolare, 1879) promoted some comparisons among different dialects and languages whose unity was partially based on the Medieval strambotto in hendecasyllabic lines, sung by heart and performed by popular singers and courtesan poets during the late Middle Ages and Renaissance. Despite any evidence that these intellectuals traced the way of folk strambotto which, migrating from Sicily to Tuscany as the cultivated poetry of the time, became the basis of the modern Italian language of Dante and Petrarch – it is necessary to remind that the Sicilian literati engaged at the court of Friedrich II wrote some poems on the patterns provided by the French trobadours, which were firstly transcribed in Bologna and then in Tuscany, thus stimulating the work of the great Tuscan poets. In view of a self-making tradition, the ethnologists and the historians of Italian literature emphasized this paradigm and transformed it into a symbol of a common origin of the Italian people. Besides the comparative method established by D’Ancona, Ermolao Rubieri distinguished three directions in creating the popular songs: songs invented by people for people as a folk level, songs composed for people as a popular level and, finally, cultivated songs adopted by the people as another type of popular genre (Storia della poesia popolare, 1877). At the end of the 19th century other researchers, influenced by Nietzche’s and d’Annunzio’s ‘philology of history’, rejected these categories, embracing the theory of folk/popular as unwritten tradition of the present and of ancient times. Ezio Levi recognized the roots of the Italian spirit in the oral poems and legends of mountebanks and lutenists, i.e. the heritage that was seen in opposition to the elitist written tradition of the court and the church, which represented a minority (Poesia di popolo e poesia di corte nel Trecento, 1915). At the same time, the ethnomusicologist Alberto Favara collected hundreds of Sicilian folk items, refusing any comparison with other Italian lands because he was not interested in the historical reconstruction and in the contaminations among cultivated and folk songs (Il canto popolare nell’arte, 1898). From this point of view, Favara applied a synchronic method showing that there has not been any change between past and present in refernce to the spontaneous creation of folk songs

La poesía en el aula de literatura : Los poetas y el canon escolar

Fil: Cavallini, Lucía. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina

Fosfiti tropos dell'acido deossicolico come leganti chirali nell'addizione coniugata asimmetrica catalizzata da Rh(I) di acidi arilboronici ad enoni.

Il presente lavoro di tesi è articolato in quattro capitoli: 1- nel primo capitolo sono illustrati gli esempi più significativi dell'utilizzo di sistemi di P(III) bidentati e monodentati come leganti chirali del Rh(I) nella reazione di addizione coniugata asimetrica di acidi arilboronici ad olefine elettron deficienti; 2- nel secondo capitolo è descritta la sintesi dei fosfiti tropos ottenuti per derivatizzazione delle posizioni 3 e 12 dell'acido deossicolico, grazie alla differente reattivirtà dei gruppi ossidrilici e la preparazione dei bifenoli 3,3' e 5,5' disostituiti; 3- il terzo capitolo riporta le prove di addizione coniugata asimmetrica di vari acidi arilboronici ad enoni ciclici catalizzata da Rh(I) utilizzando i fosfiti tropos come leganti chirali; 4- il quarto capitolo tratta la discussione della caratterizzazione stereochimaca di complessi Rh(I)-fosfito tramite spettroscopia 31P-NMR