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Preferential attachment in growing spatial networks
Luca Ferretti,Michele Cortelezzi
Computer Science , 2010, DOI: 10.1103/PhysRevE.84.016103
Abstract: We obtain the degree distribution for a class of growing network models on flat and curved spaces. These models evolve by preferential attachment weighted by a function of the distance between nodes. The degree distribution of these models is similar to the one of the fitness model of Bianconi and Barabasi, with a fitness distribution dependent on the metric and the density of nodes. We show that curvature singularities in these spaces can give rise to asymptotic Bose-Einstein condensation, but transient condensation can be observed also in smooth hyperbolic spaces with strong curvature. We provide numerical results for spaces of constant curvature (sphere, flat and hyperbolic space) and we discuss the conditions for the breakdown of this approach and the critical points of the transition to distance-dominated attachment. Finally we discuss the distribution of link lengths.
Lenalidomide in the Treatment of Chronic Lymphocytic Leukemia
Agostino Cortelezzi,Mariarita Sciumè,Gianluigi Reda
Advances in Hematology , 2012, DOI: 10.1155/2012/393864
Abstract: The application of nucleoside analogue-based chemotherapy and immunotherapy with rituximab or alemtuzumab has increased both response rate and survival in patients with Chronic Lymphocytic Leukemia (CLL). However, because none of these therapies is curative, sequential therapeutic regimens are required. The majority of patients with relapsed or refractory CLL carry poor prognostic factors and show shorter overall survival and resistance to standard treatment. Numerous drugs have recently been approved for CLL therapy and many novel agents are under clinical investigation. The role of the tumor microenvironment and of immune dysfunction in CLL have allowed to enlarge the therapeutic armamentarium for CLL patients. This article will provide a comprehensive summary regarding mechanism of action, efficacy and safety of lenalidomide in CLL patients. Relevant clinical trials using lenalidomide alone or in combinations are discussed. Lenalidomide shows good activity also in relapsed/refractory or treatment-naive CLL patients. Definitive data from ongoing studies are needed to validate overall and progression-free survival. The toxicity profile might limit lenalidomide use because it can result in serious side effects, but largely controlled by gradual dose escalation. Further understanding of the exact mechanism of action in CLL will allow more efficacious use of lenalidomide alone or in combination regimens. 1. Introduction Chronic lymphocytic leukemia (CLL) shows a remarkable heterogeneity in its clinical course, from long-term survival to fast progression and early death. Previously treated patients are known to have poor overall prognosis. In such cases, the disease almost invariably becomes resistant to various subsequent chemotherapies, leading to more toxicities and deterioration of quality of life. Fludarabine given with cyclophosphamide and rituximab is considered the cornerstone of CLL treatment, but this effective chemoimmunotherapy cannot be given with the same success to all patients. The majority of patients with relapsed or refractory CLL carry poor prognostic features, like, deletion (17p) or TP53 mutation, which are strong predictors of shorter overall survival and resistance to first-line treatment, particularly fludarabine-based regimens [1, 2]. The management of chronic lymphocytic leukemia is currently undergoing profound changes through the introduction of new therapeutic and diagnostic tools. A common feature of CLL patients is impairment of the immune system with hypogammaglobulinemia, defective function of B, T, NK cells and defective
Biosensors in Clinical Practice: Focus on Oncohematology
Nicola S. Fracchiolla,Silvia Artuso,Agostino Cortelezzi
Sensors , 2013, DOI: 10.3390/s130506423
Abstract: Biosensors are devices that are capable of detecting specific biological analytes and converting their presence or concentration into some electrical, thermal, optical or other signal that can be easily analysed. The first biosensor was designed by Clark and Lyons in 1962 as a means of measuring glucose. Since then, much progress has been made and the applications of biosensors are today potentially boundless. This review is limited to their clinical applications, particularly in the field of oncohematology. Biosensors have recently been developed in order to improve the diagnosis and treatment of patients affected by hematological malignancies, such as the biosensor for assessing the in vitro pre-treatment efficacy of cytarabine in acute myeloid leukemia, and the fluorescence resonance energy transfer-based biosensor for assessing the efficacy of imatinib in chronic myeloid leukemia. The review also considers the challenges and future perspectives of biosensors in clinical practice.
Duality between preferential attachment and static random networks on hyperbolic spaces
Luca Ferretti,Michele Cortelezzi,Marcello Mamino
Physics , 2013, DOI: 10.1209/0295-5075/105/38001
Abstract: There is a complex relation between the mechanism of preferential attachment, scale-free degree distributions and hyperbolicity in complex networks. In fact, both preferential attachment and hidden hyperbolic spaces often generate scale-free networks. We show that there is actually a duality between a class of growing spatial networks based on preferential attachment on the sphere and a class of static random networks on the hyperbolic plane. Both classes of networks have the same scale-free degree distribution as the Barabasi-Albert model. As a limit of this correspondence, the Barabasi-Albert model is equivalent to a static random network on an hyperbolic space with infinite curvature.
Direct numerical simulation of turbulent channel flow over porous walls
Marco E. Rosti,Luca Cortelezzi,Maurizio Quadrio
Physics , 2014,
Abstract: We perform direct numerical simulations (DNS) of a turbulent channel flow over porous walls. In the fluid region the flow is governed by the incompressible Navier--Stokes (NS) equations, while in the porous layers the Volume-Averaged Navier--Stokes (VANS) equations are used, which are obtained by volume-averaging the microscopic flow field over a small volume that is larger than the typical dimensions of the pores. In this way the porous medium has a continuum description, and can be specified without the need of a detailed knowledge of the pore microstructure by indipendently assigning permeability and porosity. At the interface between the porous material and the fluid region, momentum-transfer conditions are applied, in which an available coefficient related to the unknown structure of the interface can be used as an error estimate. To set up the numerical problem, the velocity-vorticity formulation of the coupled NS and VANS equations is derived and implemented in a pseudo-spectral DNS solver. Most of the simulations are carried out at $Re_\tau=180$ and consider low-permeability materials; a parameter study is used to describe the role played by permeability, porosity, thickness of the porous material, and the coefficient of the momentum-transfer interface conditions. Among them permeability, even when very small, is shown to play a major role in determining the response of the channel flow to the permeable wall. Turbulence statistics and instantaneous flow fields, in comparative form to the flow over a smooth impermeable wall, are used to understand the main changes introduced by the porous material. A simulations at higher Reynolds number is used to illustrate the main scaling quantities.
Lenalidomide in the Treatment of Lymphoproliferative Disorders and Multiple Myeloma
Anna Marina Liberati,Umberto Vitolo,Antonio Palumbo,Agostino Cortelezzi
Advances in Hematology , 2013, DOI: 10.1155/2013/812605
Abstract:
Nucleation and Growth of bundles of Single-Wall Carbon Nanotubes (C-SWNTs): the Benard-Marangoni Instability (BMI) model
F. Larouche,J. Duquette,L. Cortelezzi,N. Nigam,B. Stansfield
Physics , 2004,
Abstract: A complete explanation of the synthesis of metal-catalyst nanoparticles, and the subsequent nucleation and growth of bundles of C-SWNTs is introduced using a novel model. It is shown that the synthesis process leads to the formation of a liquid layer supersaturated in carbon surrounding each metallic-catalyst nanoparticle. The onset of a solutal B\'enard-Marangoni instability and the subsequent formation of patterns of hexagonal convection cells in the liquid layer is predicted and quantified by linear and weakly nonlinear analyses. The nucleation and growth of a C-SWNT at the center of convection cell is explained.
Features and heterogeneities in growing network models
Luca Ferretti,Michele Cortelezzi,Bin Yang,Giacomo Marmorini,Ginestra Bianconi
Computer Science , 2011, DOI: 10.1103/PhysRevE.85.066110
Abstract: Many complex networks from the World-Wide-Web to biological networks are growing taking into account the heterogeneous features of the nodes. The feature of a node might be a discrete quantity such as a classification of a URL document as personal page, thematic website, news, blog, search engine, social network, ect. or the classification of a gene in a functional module. Moreover the feature of a node can be a continuous variable such as the position of a node in the embedding space. In order to account for these properties, in this paper we provide a generalization of growing network models with preferential attachment that includes the effect of heterogeneous features of the nodes. The main effect of heterogeneity is the emergence of an "effective fitness" for each class of nodes, determining the rate at which nodes acquire new links. The degree distribution exhibits a multiscaling behaviour analogous to the the fitness model. This property is robust with respect to variations in the model, as long as links are assigned through effective preferential attachment. Beyond the degree distribution, in this paper we give a full characterization of the other relevant properties of the model. We evaluate the clustering coefficient and show that it disappears for large network size, a property shared with the Barab\'asi-Albert model. Negative degree correlations are also present in the studied class of models, along with non-trivial mixing patterns among features. We therefore conclude that both small clustering coefficients and disassortative mixing are outcomes of the preferential attachment mechanism in general growing networks.
Registros paleomagnéticos y paleontológicos en sedimentos loessoides del Pleistoceno-Holoceno en el "Estadio Ciudad de La Plata", provincia de Buenos Aires, República Argentina Palaeomagnetic and Palaeontological records in loess-like Pleistocene-Holocene sediments in the Estadio Ciudad de La Plata , Buenos Aires Province, República Argentina
J. C. Bidegain,C. R. Cortelezzi,C. A. Pittori,Y. Rico
Revista de la Asociación Geológica Argentina , 2002,
Abstract: Sedimentos de edad cuaternaria expuestos en la excavación de la obra "Estadio Ciudad de La Plata", 34o 57' 00" LS, 57o 57'40" LO, fueron estudiados mediante aplicación de la metodología paleomagnética convencional. Los vertebrados fósiles encontrados en los niveles basales de la secuencia sedimentaría corresponden a Scelidotheriinae ind., Doedicurus sp. y Panochthus intermedius, el último constituye el ejemplar más grande de Glyptodontidae registrado en la zona. De acuerdo a los datos paleomagnéticos los fósiles indicados quedan comprendidos en la zona de polaridad reversa que en el presente trabajo se asigna a la cronozona de Matuyama ( >0,78 Ma). El límite Brunhes / Matuyama se determinó a 4,6 m de profundidad desde el suelo actual. En virtud de esto, el registro sedimentario correspondiente a Brunhes es el de menor potencia obtenido para la región de La Plata. Al igual que lo observado en otras localidades de la provincia de Buenos Aires, la parte superior de la Zona Reversa de Matuyama coincide con el desarrollo de un paleosuelo (ciclo húmedo) y la parte inferior de Brunhes con condiciones de clima más seco, que dieron lugar a capas de loess y sedimentos loessoides que se asocian a estadíos glaciales en la Cordillera y Patagonia. Quaternary sediment layers exposed in a cave in the Estadio Ciudad de La Plata S 34o 57′ 00′′ W 57o 57′40′′, were studied by applying conventional palaeomagnetic methodology. Vertebrate fossils found at the base of the sedimentary sequence correspond to Scelidotheriinae ind., Doedicurus sp. and Panochthus intermedius . the last being the largest Glyptodontidae found in the area. Palaeomagnetic measurements carried out on the profile indicate that the mammal fossils occur within the Matuyama Reverse Polarity Chronozone (>0,78 Ma). The Brunhes/Matuyama boundary was identifed at 4,6 m below the surface of the present soil, so this record of the Brunhes Zone is the shortest normal polarity record obtained in the area of La Plata. Just like in other studied localities, the Upper Matuyama Polarity Zone coincides with development of soils (humidity) and the lower Brunhes is represented by loess and loess-like deposits corresponding to drier climate associated with a glacial stage in the Cordillera and Patagonia.
Different levels of taxonomic resolution in bioassessment: a case study of oligochaeta in lowland streams
Cortelezzi, Agustina;Armendáriz, Laura Cecilia;López van Oosterom, María Vanesa;Cepeda, Rosana;Capítulo, Alberto Rodrigues;
Acta Limnologica Brasiliensia , 2011, DOI: 10.1590/S2179-975X2012005000020
Abstract: aim: this study evaluated the use of oligochaetes at different levels of taxonomic resolution as environmental indicators in argentine lowland streams affected by different land uses. methods: sampling sites were grouped based on the physicochemical and habitat characteristics (low-, moderate-, and high-impact disturbance). collection of the oligochaetes samples was carried out seasonally in sediment and vegetation habitats. results: the increases in nutrients and organic matter produced elevated densities of the oligochaeta, but when the disturbance also involved changes in the physical habitat or enhancements in toxic substances, the abundance decreased significantly to values even lower than those of non-impacted environments. the responses of naidinae and tubificinae were similar. the density of the pristininae decreased with increasing impact, but those of the enchytraeidae and rhyacodrilinae increased at the most highly impacted sites. the opistocystidae were not recorded in high-impact sites. species richness and diversity (h') were lower in high-impact sites and even lower in sediments. some species presented no restrictions in the habitat type or with the contamination level: limnodrilus hoffmeisteri, dero furcatus, d. digitata, d. pectinata, pristina longiseta, and p. aequiseta. moreover, trieminentia corderoi, slavina appendiculata, and aulodrilus pigueti exhibited the highest abundances at low-impact sites and were not registered in high-impact sites. conclusions: the oligochaeta show a relatively wide ecological valence through their extensive number of species. although lower taxonomic levels can give information about environmental status, test-species' sensitivities to different types and degrees of contamination will be of utmost relevance to the evaluation of ecological quality.
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