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Large deviations for generalized polya urns with general urn functions
No full textWe consider a generalized two-colorPolya urn (black and
withe balls) first introduced by Hill, Lane, Sudderth, where the urn
composition evolves as follows: let : [0; 1] ! [0; 1], and denote
by xn the fraction of black balls at step n, then at step n + 1
a black ball is added with probability (xn) and a white ball is
added with probability 1 (xn). We discuss large deviations
for a wide class of continuous urn functions. In particular, we
prove that this process satis es a Sample-Path Large Deviations
principle (SPLDP), also providing a variational representation for
the rate function. Then, we derive a variational representation for
the limit (s) = limn!1
1
n log P (fnxn = bsncg) ; s 2 [0; 1] ; where
nxn is the number of black balls at time n, and use it to give
some insight on the shape of (s). Under suitable assumptions on
we are able to identify the optimal trajectory. We also find a
non-linear Cauchy problem for the cumulant generating function
and provide an explicit analysis for some selected examples. In
particular, we discuss the linear case, which is strictly related to
the so-called Bagchi-Pal urn, giving the exact implicit expression
for in therms of the Cumulant Generating Function
Analysis and interpretation of Carbon ion fragmentation in the Bragg peak energy range
No full textHadrontherapy is the treatment of tumours with Protons (p), or heavier ions like
Carbon (C) and Oxygen (O). It is based on the fact that ionising radiation is used
to kill tumour cells. One of the advantages of heavy ions compared to conventional
radiotherapy is the characteristic behaviour of the energy deposition, which peaks
only when the particles are very close to the stopping point, called Bragg peak. The
Hadrontherapy is becoming one of the main therapies for the treatment of some
malignant neoplasms. Compared to Proton therapy, C therapy has considerable
advantages, even though C ions could fragment.
In this work the exclusive quasi-elastic fragmentation reaction 12C+x !8 Be+
is studied at the energy of 33MeVu−1 of projectiles, which is the dominant reaction
at this energy. The importance of this energy domain relies on the fact that it is
the typical value where the fast rise of the energy deposition starts, just before the
Bragg peak.
Different target materials, namely Carbon, Gold and Niobium, have been used
in the present work. In all the cases a contamination of H in the targets has been
found. This contamination observed explains the excess of high energy a in the data.
The reaction responsible for such an excess, 12C + p !9 B + , has been added to
the FLUKA Monte Carlo simulation (MC) code as a pre-equilibrium stage channel
of the (p,a) reaction.
The identification and the description of the pre-equilibrium reaction in the
MC allowed a significant improvement in the comparison between data and MC.
This allowed to identify and reduce the background due to the H contamination in
the process under investigation and measure its cross section as a function of the
fragments’ energy and emission angles
Nonlinear light beam propagation in reorientational nematic liquid crystals
No full textLiquid crystals (LC) are excellent media for the exploration of nonlinear phenomena, particularly due to their high and nonlocal response to electric and magnetic fields. Besides the fundamental interest, the field-induced reorientation of LC molecules is widely used in display applications and is promising for optical signals processing such as attenuators, tunable lens and smart-windows. Recently, a great deal of attention has been dedicated to spatial (2+1)D optical solitons in nematic liquid crystals, the so called nematicons. Nematicons are diffractionless self-confined light beams, that is, guided by their own waveguide
in the dielectric. Specifically, diffraction is balanced out by self-focusing through the reorientational nonlinearity. Moreover, owing to the highly nonlocal character of the response, nematicons are stable and robust to external perturbations. Being self-induced graded-index guides for co-polarized signals, nematicons are an avenue to a wide range of all-optical devices and reconfigurable routers. When the electric field and the average alignment of molecules are normal to each other, the reorientational response presents a threshold in power before the material properties get modified by the impinging light. This dissertation deals with the investigation of beam self-trapping near such threshold in nematic liquid crystals, a configuration scarcely explored in the existing literature. The first chapter introduces the main features of liquid crystals and of nematicons in threshold-free geometries, including self-focusing, self-trapping and self-steering. Tthe second chapter discusses how self-focusing in the presence of threshold provides optical bistability and hysteresis in beam width versus power, due to step-like nonlinear response with excitation. This is indeed the first report on bistability with propagating beams and the first experimental demonstration of soliton bistability. The third chapter studies nematicon propagation near the threshold, in bias-free cells allowing the direct observation of beam-walk-off: combining self-steering and the inherent anisotropy of liquid crystals, the system is capable of switching from positive to negative refraction as power changes. This is the first demonstration of such a power controlled transition in refraction, which, besides the other, allows optimizing all-optical
routers based on nematicons, as optical self-steering is maximized
Regolazione del quorum sensing e della virulenza in Pseudomonas aeruginosa
No full textThe asocial existence of the bacterial cells has been a major paradigm in microbiology for a long time. However, a huge amount of experimental evidences collected in the last 30 years has revealed that bacteria preferentially live in communities, in which the behavior of individual cells is coordinated by cell-cell communication systems to control phenotypic behaviors at the population level. Bacteria not only form well-organized communities, but they also exploit complex social cooperative and competitive interactions, mimicking multicellular organisms. Bacterial social life mainly relies on their ability to exchange information via chemical communication systems. In some cases, these systems allow a group of bacteria to trigger a unified and coordinated response to metabolic and environmental stimuli, so to accomplish tasks which would be difficult, if not impossible, to achieve for individual bacterial cells. One of the most studied bacterial cell-cell communication systems is quorum sensing (QS), by which a bacterial population coordinately reprograms gene expression in response to cell density. The QS-response is achieved when the concentration of a specific signal molecule, produced and secreted by single bacteria cells, reaches a threshold level, corresponding to a certain cell density, at which it is able to trigger a phenotypic and behavioral change in all the members of the bacterial population. QS in different bacteria is involved in the regulation of a wide variety of physiological processes, including competence, bioluminescence, antibiotic biosynthesis, motility, plasmid conjugal transfer, biofilm formation, and production of bacterial virulence factors in plant, animal and human pathogens. Furthermore, evidence has been accumulated that some bacterial signal molecules are used not only for intra-species communication, but also to exchange information between bacteria of different species or genera occupying the same ecological niche, and also to interact with their eukaryotic hosts. The QS system of the opportunistic human pathogen Pseudomonas aeruginosa is one of the best characterized bacterial communication systems, and it is now considered as a mayor model system for QS studies. In P. aeruginosa QS positively controls the expression of virulence related traits, such as virulence factor production and biofilm formation, and it is consequently involved in both acute and chronic infections. Moreover the QS circuit of P. aeruginosa is one of the most complex communication systems described up to date, since it is made up of four interconnected QS systems interwoven in an intricate regulatory network, the las, rhl, pqs and IQS systems. The four QS systems of P. aeruginosa are hierarchically organized and, in a wide range of cultural conditions, the las system is at the top of this hierarchy, being required for full activation of the other three QS circuits. Overall, the las QS system positively controls the complex regulative cascade involved in the expression of virulence-related phenotypes in P. aeruginosa, and for this reason it is considered one of the most promising target for the development of new anti-virulence drugs. Besides cell density, the las QS system is modulated by many regulators and signalling systems in response to metabolic and environmental cues. In particular, the timing and the extent of the QS response are finely modulated at different levels by a plethora of transcriptional and post-transcriptional regulators. It is believed that this fine-tuning of the las QS system might play a major role during P. aeruginosa infections, even though this hypothesis has been poorly investigated in mammalian models of infection so far.
Despite in the last 20 years the huge efforts of the scientific community has lead to a refined knowledge of the molecular mechanisms controlling the expression of the las QS system in P. aeruginosa, our understanding of its regulation and actual role in the infection processes is far from complete. On these bases, the main aim of this PhD project has been to contribute to shed light on some unclear aspects of the las QS system regulation. In particular, this PhD work aimed at (i) identifying novel transcriptional regulators of the las QS system; (ii) evaluating the effect of a dysregulation in the timing and the extent of the las QS response on the ability of P. aeruginosa to establish both acute and chronic infections in a murine model system; (iii) investigating new emerging behavioral properties arising from the peculiar regulatory architecture of the las QS system. Briefly, the search for novel direct regulators of LasR, the QS signal molecule receptor that activates the las QS system, lead to the identification of a new QS transcriptional regulator PA3699. This protein directly represses lasR transcription, and consequent expression of QS-controlled virulence phenotypes in P. aeruginosa. The study of the effect of a dysregulation in the timing and extent of the QS response revealed that an anticipated activation of the las QS system does not significantly affect P. aeruginosa virulence in a mouse model of infection, while an increased activation of the las QS system beyond physiological levels impairs P. aeruginosa ability to establish chronic lung infections in mice. The arrangement of the genes composing the las QS system resembles the architecture of a network motif, the type-1 incoherent feedforward loop (IFFL-1), which is known to confer peculiar regulatory properties to the expression of its output genes. In line with this resemblance, we demonstrated that the las IFFL-1 confers robustness to the expression of its output genes with respect to possible fluctuations in the levels of the LasR activator. The main achievements of this PhD work have been published in two international peerreviewed journals (Longo et al., 2013; Bondí et al., 2014), and have been collected in an additional manuscript almost ready to be submitted (Bondí et al., manuscript in preparation)
Enseigner les langues nationales à Djibouti, une autre approche!
No full textQoraagu wuxuu halkan ku falanqaynayaa arrinta wax ku baridda luqadaha qaranka ee dalalka Afrika oo inta hadan aan aad loo qiimayn sida loo qaddariyo luqadaha qolooyinka horay dad gumaysaty. Gaar ahaan wuxuu baarayaa afafka Jabuuti, oo ah af Soomaali iyo af Cafar, wuxuuna soo jeedinayaa talooyin cusub oo la xiriira tabtii labada af loogu biirin karo nidaamka waxbarashada dalka Jabuuti.L'autore approfondisce la questione dell'insegnamento delle lingue nazionali nei paesi africani che spesso godono di minor prestigio rispetto alle lingue degli ex paesi colonizzatori. In particolare, analizza il caso delle lingue di Gibuti, somalo e afar, e propone un approccio innovativo per promuovere il loro ingresso reale nel sistema educativo gibutino.The author deals with the issue of teaching national languages in those African countries where these languages are lower in status compared to the former colonizing countries' languages. In particular, he analyses the case of Djibouti languages, Somali and Afar, and proposes a new approach to promote their actual introduction in the Djiboutian educational system.Cabdirashid M. Ismaaciil, Cabdalla C. Mansuur, Saynab A. Sharci (eds.
[Somalia]
No full textImmagine messa a disposizione dalla Società Geografica Italiana.Sawir ay soo diyaarisay Shirkadda Juqraafiyeed ee Taliyaaniga.Image provided by the Italian Geographical Society.Link: http://www.societageografica.it/opac/scheda1.php?id=24027&s=
[Poster 64]
No full textDokumentigan waxaa dadka u soo bandhigay "The Digital Somali Library", ee jaamacadda "Indiana University".Documento messo a disposizione dalla Digital Somali Library, Indiana University.Document provided by the Indiana University's Digital Somali Library.Link: http://www.indiana.edu/~libsalc/african/Digital_Somali_Library/history.htm
[Dhirta VIII - Piante VIII]
No full textHalkan odayaashu waxay aad uga hadlayaan dhirta daaqa, gaar ahaan, dhirta uu geelu jecelyahay, dhirta aan jeclayn iyo dhirta ay u keento dhibaato iyo cudurro xoolaha daaqa. Odayaashu waxay kaloo ka hadlayaan gobollada dhirta ka soo jeeddo iyo ereyada la xiriira arrintan.In questa conversazione gli anziani parlano approfonditamente delle piante da pascolo: in particolare descrivono quali piante sono gradite dai cammelli, quali sono evitate, quali sono portatrici di malesseri o malattie agli animali che se ne nutrono. Gli anziani inoltre indicano le zone di provenienza delle piante e presentano la terminologia relativa all'argomento.In this conversation the elders talk extensively about pasture plants: in particular they illustrate the plants loved by the camels, the ones which are avoided, the ones which bring illnesses or diseases to the animals. The elders also indicate the place of origin of the plants and present the terminology related to the subject.Haasaawe badan oo laga duubay siddeetameeyadii odayaal ka shaqaynaayay Akadeemiyada Cilmiga, Fanka iyo Suugaanta ee Muqdisho, iyagoo ka hadlaya hiddaha iyo dhaqanka ee bulshada soomaaliyeed.Registrazioni audio di conversazioni intercorse tra anziani dell'Accademia delle Scienze, delle Arti e della Letteratura di Mogadiscio negli anni '80, su temi relativi alla cultura e alla società tradizionali somale.Conversations between Elders of the Academy of Science, Arts and Literature on arguments related with Somali culture, society and traditions, recorded in Mogadishu in the 80's
[Geel IV - Cammello IV]
No full textHaasaawahanna waxay odayaashu kaga hadlayaan waxyaabo la xiriira xoolaha (geela, lo'da iyo ariga)sida: habka abaahinta, rimidda, dhiciska, marxaladaha kala duwan ee korritaanka xoolaha iyo ereyo la xiriira arrimahaas.In questa conversazione gli anziani si occupano di alcuni aspetti relativi al bestiame (cammelli, ovini e caprini): le modalità di accoppiamento, la gravidanza, l'aborto, il parto e la nascita prematura, i diversi stadi di crescita degli animali, soffermandosi inoltre sul lessico relativo.In this conversation, the elders talk about some aspects related to livestock (camels, sheep and goats): mating, pregnancy, abortion, birth and premature birth, the different moments of animals' growth; moreover they linger on the lexicon related to the subject.Haasaawe badan oo laga duubay siddeetameeyadii odayaal ka shaqaynaayay Akadeemiyada Cilmiga iyo Fanka iyo Suugaanta ee Muqdisho iyagoo ka hadlaya hiddaha iyo dhaqanka ee bulshada soomaaliyeed.Registrazioni audio di conversazioni intercorse tra anziani dell'Accademia delle Scienze, delle Arti e della Letteratura di Mogadiscio negli anni '80, su temi relativi alla cultura e alla società tradizionali somale.Conversations between Elders of the Academy of Science, Arts and Literature on arguments related with Somali culture, society and traditions, recorded in Mogadishu in the 80's
