7,168 research outputs found
Concentration fluctuations in aquifer transport: A rigorous first-order solution and applications
No full textFlow and transport take place in a formation of spatially variable conductivity K(x). The latter is modeled as a lognormal stationary random space function. With Y = ln K, the structure is characterized by the mean [Y], the variance sigma(Y)(2), the horizontal and vertical integral scales I-h and I-v. The fluid velocity field V(x), driven by a constant mean head gradient, has a constant mean U and a stationary two-point covariance. Transport of a conservative solute takes place by advection and by pore-scale dispersion (PSD), that is assumed to be characterized by the constant longitudinal and transverse dispersivities alpha(dL) and alpha(dT). The local solute concentration C(x, t), a random function of space and time, is characterized by its statistical moments. While the mean concentration [C] was investigated extensively in the past, the aim here is to determine the variance sigma(C)(2), a measure of concentration fluctuations. This is achieved in a Lagrangean framework, continuous limit of the particle-tracking procedure, by adopting a few approximations. The present study is a continuation of a previous one (Dagan, G., Fiori, A., 1997. The influence of pore-scale dispersion on concentration statistical moments in transport through heterogeneous aquifers. Water Resour. Res., 33, 1595-1606) and extends it as follows: (i) it is shown that the indepence of the advective component of a solute particle trajectory from the trajectory component associated with PSD, is a rigorous first-order approximation in sigma(Y)(2). This independence, that was conjectured in the work of Dagan and Fiori (Dagan, G., Fiori, A., 1997. The influence of pore-scale dispersion on concentration statistical moments in transport through heterogeneous aquifers. Water Resour. Res., 33, 1595-1606), simplifies considerably the solution; (ii) the covariance of two-particle trajectories, needed in order to evaluate sigma(C)(2), is rederived, correcting for an error in the previous work. The general results are applied to determining CVC = sigma(C)/[C] at the center of a small solute body, of initial size much smaller than I-h = I-v, as function of sigma(gamma)(2), t' = tU/I and Pe = UI/D-dT = I/alpha(dT). Though PSD reduces considerably CVC as compared with advective transport (Pe = infinity), its value is still quite large for time intervals of interest in applications. This finding is in agreement with the analysis of field data by Fitts (Fitts, C.R., 1996. Uncertainty in deterministic groundwater transport models due to the assumption of macrodispersive mixing: evidence from the Cape Cod (Massachussets, USA) and Borden (Ontario, Canada) tracer tests. J. Contam. Hydrol., 23, 69-84). (C) 2000 Elsevier Science B.V. All rights reserved
OPTIMIZATION OF A CONTROL LAW TO SYNCHRONIZE FIRST-ORDER DYNAMICAL SYSTEMS ON RIEMANNIAN MANIFOLDS BY A TRANSVERSE COMPONENT
No full textThe present paper builds on the previous contribution by the second author, S. Fiori, Synchronization of first-order autonomous oscillators on Riemannian manifolds, Discrete and Continuous Dynamical Systems – Series B, Vol. 24, No. 4, pp. 1725 – 1741, April 2019. The aim of the present paper is to optimize a previously-developed control law to achieve synchronization of first-order non-linear oscillators whose state evolves on a Riemannian manifold. The optimization of such control law has been achieved by introducing a transverse control field, which guarantees reduced control effort without affecting the synchronization speed of the oscillators. The developed non-linear control theory has been analyzed from a theoretical point of view as well as through a comprehensive series of numerical experiments
La gerarchia come criterio di verità: 'boni' e 'mali' nel processo romano arcaico
No full textIn archaic Roman law, the defendant in a civil trial could not be acquitted, even in the absence of any proofs, unless he had the same or a better social standing than the plaintiff. This rule has nothing to do with an irrational basis of the archaic trial, but is perfectly consistent with the Roman vision of the socio-cosmic order as hierarchical. A person of high rank (a 'bonus') was believed to be more trustworthy (to have more 'fides') than one from the lower classes (a 'malus'), and this rule applied not only to the witnesses but also to the parties of the trial
A Construction and Characterization of New Sharply 3-Transitive Permutation Sets Contained in PΓL(2 , K)
No full textGrafi cubici e gruppi di automorfismo
No full textIn questa presentazione esporremmo alcuni risultati riguardanti automorfismi di grafi cubici, come ad esempio: a) alcune condizioni per le quali un automorfismo di un grafo agisce su particolari sottografi come l'automorfismo banale o un automorfismo non banale; b) l'esistenza di cinque famiglie infinite che soddisfano le condizioni di cui sopra; c) la determinazione dei gruppi di automorfismo di sette famiglie infinite di grafi cubici connessi con girth 5, cinque delle quali costituite da grafi detti snarks; d) per ogni intero positivo m, l'esistenza di grafi cubici (snarks) con 24+4m o 26+4m vertici aventi gruppi di automorfismi banali, di un grafo cubico con 24+4m vertici avente gruppo di automorfismo isomorfo al gruppo ciclico di ordine 2, di un grafo cubico con 18+16m vertici avente gruppo di automorfismo di ordine 2^{m+2}; e) per ogni intero positivo dispari k, k>3, l'esistenza di un grafo cubico (snarks) di ordine 4k ed un grafo cubico (snark) di ordine 8k con gruppo di automorfismo isomorfo al gruppo diedrale di ordine 4k
Piani formalmente euclidei
No full textIn the last decacìes, university teaching has introduced Geometry as a chapter of Linear Algebra. This implies that geometrical culture and spacial intuition are more and more lacking in the new gcnerations of graduated in Mathematics, which of course has a negative feedback on the qualitv of mathematics teaching and its educational value. So it is important to show the links existing between the synthetic and the analytic approach to the geometry. In this paper we offer a very generai way that, bearing in mind the development of geometrical thought in the last two centuries, allows to shift from one setting to the other. Such procedure, which doesn't depend on the axioms of order nor on those of congruence (and which therefore is not necessarily linked to the field of real numbers), allows to extend to a wide class ofplanes (incÌuding the Eiiclidean one) the notions of similitude and isometry and to find out and claracterize their equations
Redox state of magmas and granite-related Mo mineralization: evidences from Late Variscan F- bearing granites from Southern Sardinia (Italy)
No full textRedox state of magmas has been invocated to explain the metallogenic behaviour of intrusive magmatism (Ishihara,
1981). Thus, Sn deposits are linked to low-fO2, ilmenite series, while Mo deposits are better bracketed into high-fO2,
magnetite series. In Variscan Europe Mo deposits are represented in a few districts, including Eastern Erzgebirge,
France and Sardinia. In Sardinia, small Mo deposits are related to a post-collisional F-bearing granite suite dated close
to 290 Ma by Re/Os on molybdenite (Boni et al., 2003) and 40Ar/39Ar on biotite (Dini et al., 2005). This late Variscan
suite is dominated by metaluminous biotite leucogranites grading to hololeucratic microgranitic to granophyric
varieties; amphibole biotite monzogranites are locally observed (Monte Sette Fratelli). They emplaced at shallow crustal
levels and locally (Ogliastra) grade to felsic volcanics. Thermal effects of the intrusions are limited to narrow contact
aureolas (andalusite zone) around the plutons. In SW Sardinia (Sulcis and Monte Linas intrusions), both Mo and Sn
deposits occur. Magmatic bodies show a distinctive magmatic zonation, with medium-grained granites dimembered
upward by thick, flat-lying fine-grained to porphyritic varieties, including fayalite-bearing pegmatite layers. Finegrained
to porphyritic rocks suffered various degrees of greisening, and host Mo ores, related to numerous small endoand
exo- quartz-muscovite greisens (e.g. Perda Lada), grading to quartz vein and stockwork systems (Perd'e Pibera, Su
Seinargiu, Flumini Binu). Ores are commonly dominated by molybdenite, with subordinate pyrite, chalcopyrite and
wolframite. The studied deposits are related to ilmenite rock -series, as evidenced by petrography (opaque contents of
granites <1%; ilmenite>>magnetite), and confirmed by geochemical ratios (Rb/Sr, FeO/Fe2O3, K/Rb). This behavior
seems to contrast with the Mo/magnetite series association, and is more coherent with the presence of Sn vein deposits
in the same areas (Naitza et al. 2015). A possible explanation involve changes of physicochemical parameters (in
particular, fO2 and HF activity) from magmatic processes during magma emplacement to greisening; variation of redox
conditions are confirmed by discontinuous reverse zoning of plagioclase laths in fine-grained facies, indicating a
progressive PH2O increase with magmatic evolution. Mineralization prevalently occurred in close system conditions,
although in some areas (Oridda, Su Seinargiu, Flumini Binu) Mo ores are centered on bodies of porphyritic rocks,
showing features close to porphyry-style mineralization (Fiori et al., 1986).
Boni M., Stein H.J., Zimmerman A. & Villa I.M. 2003. Re-Os age for molybdenite from SW Sardinia (Italy): a
comparison with 40Ar/39Ar dating of Variscan granitoids. In: Eliopulos K. et al., Eds., Mineral exploration and
sustainable development. Millpress, Rotterdam, 247-250.
Dini A., Di Vincenzo G., Ruggieri G., Rayner J. & Lattanzi P. 2005. Monte Ollasteddu, a new gold discovery in the
Variscan basement of Sardinia (Italy): first isotopic (40Ar-39Ar, Pb) and fluid inclusion data. Miner. Deposita, 40,
337-346.
Fiori M., Garbarino C., Padalino G. & Masi U. 1986. Chemical features of wallrocks from Mo-showings of Sardinia
(Italy). Rend. Soc. It. Mineral. Petrol., 41, 25-39.
Ishihara S. 1981. Granitoid series and mineralization. Economic Geology, 75th anniversary volume, 458-484.
Naitza S., Secchi F., Oggiano G. & Cuccuru S. 2015.
Multi-vehicle assignment with elastic vehicle choice behaviour: Fixed-point, deterministic process and stochastic process models
No full textNew types of vehicles, such as electricity-powered and/or autonomous cars or buses, are under rapid development, but the time needed to turn the existing stock of traditional vehicles, such as privately-owned human-driven fossil fuelled passenger cars, will likely last several years during which mixed traffic is expected. Moreover, the likely effects of the introduction of such vehicles may not be necessarily positive. Thus, a careful analysis of their various impacts through well designed tools is needed. Main tools for transportation systems analysis are based on methods for travel demand assignment to a transportation network, commonly used to support transportation project assessment and evaluation. The original contribution of this paper is twofold. First, a modelling approach to multi vehicle type assignment is proposed, in this approach the user choice proportions among vehicle types available to users are the results of an explicit choice behaviour model instead of input data as in all existing papers on multi-vehicle assignment. This approach is applied for analysing assignment to transportation networks including Fixed-Point models for equilibrium assignment and Deterministic and Stochastic Process models for day-to-to dynamic assignment. Second, statistical methods are introduced to study the bifurcation of SP models, in order to account for the stochasticity of such models. In particular, the Hartigan's Dip statistic, which measure the degree of unimodality of a distribution, showed to be the most effective one in identifying bifurcation in SP models. Fixed-point stability and bifurcation analysis are carried out too, and some simple numerical examples are also discussed. Reported results show that innovative vehicles with less impact on congestion than traditional ones may not have a positive effect on equilibrium stability since negative effect of reducing route choice dispersion may be compensate the positive effects on congestion
Micromosaico. Storia, tecnica, arte del mosaico minuto romano
No full textIl mosaico minuto o micromosaico nacque a Roma nella seconda metà del ’700 e il periodo di maggiore produzione di questo tipo di artigianato artistico è quello che va dalla fine di tale secolo a tutto l’800. Nella seconda metà del ’500 era partito il grande progetto di decorare a mosaico le volte di San Pietro e di tradurre a mosaico opere pittoriche della stessa basilica, utilizzando materiali vetrosi, detti anche smalti, di vario colore. Questi ultimi erano prodotti a Venezia, ma presto si cominciò a prepararli anche a Roma. In tale contesto, si iniziò a produrre, anche all’interno dello Studio Vaticano del Mosaico, il micromosaico fatto con tessere di piccole dimensioni. Il vetro usato veniva filato in sottili bacchette da cui venivano ricavate le minuscole tessere. Il supporto su cui veniva composto il micromosaico poteva essere di metallo, quale una lamina di rame con bordi rialzati, o una lastrina di pietra con un incavo o di altro tipo, in cui venivano assemblate le piccole tessere fissandole con un opportuno legante. Le stesse opere avevano dimensioni ridotte, eseguite con grande precisione e rifinite con altrettanta cura e potevano essere inserite, ad esempio, su manufatti quali tavolini con piano di marmo, tabacchiere, fermacarte, ecc., o addirittura costituivano spille e gioielli, quando venivano applicati in oreficeria
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