104,121 research outputs found
Existence of stationary turbulent flows with variable positive vortex intensity
No full textWe prove the existence of stationary turbulent flows with arbitrary positive vortex
circulation on non-simply connected domains. Our construction yields solutions for
all real values of the inverse temperature with the exception of a quantized set, for
which blow-up phenomena may occur. Our results complete the analysis initiated
in Ricciardi and Zecca (2016)
Lectures in Applied Mathematics and Informatics
No full textA collection of lectures written by well-known specialist in a variety of fields within applied mathematics: 1. Analysis of algorithms (P. Cull) 2. Rational and recognizable subsets (J.E. Pin) 3. On generalizes entropies with applications (I.J. Taneja) 4. Diffusion process and first-passage-time (L.M. Ricciardi; S. Sato) 5. Functionals of Brownian motion (T. Hida
Lectures in Applied Mathematics and Informatics
No full textA collection of lectures written by well-known specialist in a variety of fields within applied mathematics: 1. Analysis of algorithms (P. Cull) 2. Rational and recognizable subsets (J.E. Pin) 3. On generalizes entropies with applications (I.J. Taneja) 4. Diffusion process and first-passage-time (L.M. Ricciardi; S. Sato) 5. Functionals of Brownian motion (T. Hida
The capacitated transshipment location problem with stochastic handling utilities at the facilities
No full textThe problem consists in finding a transshipment facilities location that maximizes the total net utility when the handling utilities at the facilities are stochastic variables, under supply, demand, and lower and upper capacity constraints. The total net utility is given by the expected total shipping utility minus the total fixed cost of the located facilities. Shipping utilities are given by a deterministic utility for shipping freight from origins to destinations via transshipment facilities plus a stochastic handling utility at the facilities, whose probability distribution is unknown. After giving the stochastic model, by means of some results of the extreme values theory, the probability distribution of the maximum stochastic utilities is derived and the expected value of the optimum of the stochastic model is found. An efficient heuristics for solving real-life instances is also given. Computational results show a very good performance of the proposed methods both in terms of accuracy and efficienc
Metodi analitici e computazionali nella risoluzione del problema del tempo di primo passaggio per processi diffusivi e di Gauss
No full textNel 1971 ad opera di Blake e Lindsey compare un articolo di rassegna nel quale si illustrano alcuni problemi, collegati alla dinamica di certi processi stocastici, non ancora del tutto risolti. Uno di questi è quello che gli autori chiamano “level-crossing problem” che è relativo alla determinazione di proprietà probabilistiche del tempo T necessario ad un processo per raggiungere per la prima volta una (o una di due) barriera in generale essa stessa dipendente dal tempo. Nel medesimo articolo gli autori espongono i risultati all’epoca noti e le tecniche che usualmente venivano impiegate per affrontare il problema. La conclusione a cui essi pervengono è che la soluzione completa della questione, ossia la determinazione della funzione di densità di probabilità di T è ottenibile solo quando, con opportuna trasformazione spazio-temporale ci si riconduce al processo di Wiener e a una barriera lineare. Nel caso generale o si ricorre alla stima di importanti indici di T oppure si tenta di ottenere maggiorazioni o minorazioni per la probabilità che il primo passaggio avvenga prima di un assegnato istante. Successivamente, nel 1986, Abrahams ha aggiornato la rassegna di Blake e Lindsey, ma, come l’autrice stessa fa notare, relativamente al “level-crossing problem” pochi furono i risultati nel frattempo individuati; tra questi, la Abrahams cita quelli relativi a processi di gauss non markoviani con contributi da Durbin e da Ricciardi. Nella presente tesi di dottorato il problema del tempo di primo passaggio viene analizzato relativamente ai processi di diffusione e a processi di Gauss non markoviani. Per i primi viene determinata una equazione integrale di Volterra di seconda specie avente per incognita la funzione di densità di probabilità di T : la sua utilità consiste nella presenza del suo nucleo di una funzione arbitraria la cui opportuna specificazione consente di ottenere tutte le soluzione analitiche note. In più, la funzione arbitraria può essere scelta in modo da rendere il nucleo nullo sulla bisettrice del primo quadrante e questo elimina la singolarità presente invece in altre equazioni integrali in precedenza individuate. Tale proprietà consente di ottenere semplici ed efficaci procedure di calcolo numerico atte ad essere utilizzate, con tempi ragionevolmente piccoli, in problemi di identificazione e stima dei parametri. Lo stesso tipo di analisi viene presentato anche relativamente al caso del problema con due barriere. Relativamente ai processi di Gauss non markoviani viene presentato un metodo Monte Carlo utilizzabile senza l’ausilio di dispositivi fisici che differenti autori hanno utilizzato in precedenti proposte dello stesso tipo
CD14 is Expressed by Subsets of Murine Dendritic Cells and Upregulated by Lipopolysaccharide
No full textMahnke K, Becher E, Ricciardi-Castagnioli P, Schwarz T, Luger T, Grabbe S. CD14 is Expressed by Subsets of Murine Dendritic Cells and Upregulated by Lipopolysaccharide. In: Ricciardi-Castagnoli P, ed. Dendritic Cells in Fundamental and Clinical Immunology. Advances in Experimental Medicine and Biology. Vol 417. Boston, MA: Springer US; 1997: 145-159
Predators vs. alien: differential biotic resistance to an invasive species by two resident predators
No full textThe success of invading species can be restricted by interspecific interactions such as competition and predation (i.e. biotic resistance) from resident species, which may be natives or previous invaders. Whilst there are myriad examples of resident species preying on invaders, simply showing that such an interaction exists does not demonstrate that predation limits invader establishment, abundance or spread. Support for this conclusion requires evidence of negative associations between invaders and resident predators in the field and, further, that the predator-prey interaction is likely to strongly regulate or potentially de-stabilise the introduced prey population. Moreover, it must be considered that different resident predator species may have different abilities to restrict invaders. In this study, we show from analysis of field data that two European predatory freshwater amphipods, Gammarus pulex and Gammarus duebeni celticus, have strong negative field associations with their prey, the invasive North American amphipod Crangonyx pseudogracilis. This negative field association is significantly stronger with Gammarus pulex, a previous and now resident invader in the study sites, than with the native Gammarus duebeni celticus. These field patterns were consistent with our experimental findings that both resident predators display potentially population de-stabilising Type II functional responses towards the invasive prey, with a significantly greater magnitude of response exhibited by Gammarus pulex than by Gammarus duebeni celticus. Further, these Type II functional responses were consistent across homo- and heterogeneous environments, contrary to the expectation that heterogeneity facilitates more stabilising Type III functional responses through the provision of prey refugia. Our experimental approach confirms correlative field surveys and thus supports the hypothesis that resident predatory invertebrates are differentially limiting the distribution and abundance of an introduced invertebrate. We discuss how the comparative functional response approach not only enhances understanding of the success or failure of invasions in the face of various resident predators, but potentially also allows prediction of population- and community-level outcomes of species introductions
From Nonlinear Integrated Optics to Microresonator Frequency Combs
No full textPerhaps one of the most spectacular current applications of nonlinear integrated optics, a field
which was pioneered by George Stegeman more than thirty years ago [1], is that of nonlinear
microresonator based optical frequency comb light sources. Optical frequency comb sources are
characterized by a spectrum comprising many equally spaced components [2], and have a wide
range of scientific and technological applications. Although commercial comb generators are based
on mode-locked lasers and fiber supercontinuum generation, nonlinear integrated optics provides a
low-cost and chip-scale alternative, based on a low-power cw laser coupled into a high-Q
microresonator [3]. So far microresonator frequency combs have exploited the third order “Kerr”
nonlinearity, which permits to generate successive comb lines with a spacing equal to the resonator
free-spectral range via cascaded four-wave mixing [4-5]. Modeling of microresonator frequency
combs can be greatly simplified by a single partial differential equation approach [4-6], analogous
to the case of other coherently driven Kerr spatially diffractive [7] or temporally dispersive [8-9]
nonlinear cavities. In order to lower the threshold power and extend the spectral range of frequency
comb generation, for example into the visible or mid-infrared, while still using near-infrared cw
laser pumps, quadratic nonlinear cavities can be exploited [10]. These quadratic microresonator
frequency comb sources operate close to the phase-matching condition for the underlying quadratic
processes, and not in the cascading regime that reduces the dynamics to the Kerr case [11]. Quite
remarkably, a single time domain partial differential equation with an effective delayed third-order
nonlinearity was derived to describe with excellent accuracy the dynamics of quadratic frequency
comb generation [12-13]. In situations where multiple processes are present, and the frequency
combs generated around the interacting waves over multiple octaves overlap, we carried out
numerical modeling based on a single envelope equation approach [14].
References
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[3] P. Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, and T. J. Kippenberg, Nature 450, 1214 (2007).
[4] S. Coen, H. G. Randle, T. Sylvestre, and M. Erkintalo, Opt. Lett. 38, 37 (2013).
[5] T. Hansson, D. Modotto, and S. Wabnitz, Phys. Rev. A 88, 023819 (2013).
[6] T. Hansson, D. Modotto, and S.Wabnitz, Opt. Comm. 312, 134 (2014).
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[8] M. Haelterman, S. Trillo, and S. Wabnitz, Opt. Commun. 91, 401 (1992).
[9] F. Leo, S. Coen, P. Kockaert, S.-P. Gorza, P. Emplit, and M. Haelterman, Nature Photon. 4, 471 (2010).
[10] I. Ricciardi, S. Mosca, M. Parisi, P. Maddaloni, L. Santamaria, P. De Natale, and M. De Rosa, Phys. Rev. A 91,
063839 (2015).
[11] G. I. Stegeman, D. J. Hagan, and L. Torner, Optical and Quantum Electronics 28, 1691 (1996).
[12] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. Lett. 116, 033901
(2016).
[13] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. A 93 (2016).
[14] T. Hansson, F. Leo, M. Erkintalo, J. Anthony, S. Coen, I. Ricciardi, M. De Rosa, and S. Wabnitz, J. Opt. Soc. Am.
B 33, 1207 (2016)
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