Cardinality versus q-Norm Constraints for Index Tracking

Index tracking aims at replicating a given benchmark with a smaller number of its constituents. Different quantitative models can be set up to determine the optimal index replicating portfolio. In this paper, we propose an alternative based on imposing a constraint on the q-norm, 0 < q < 1, of the replicating portfolios’ asset weights: the q-norm constraint regularises the problem and identifies a sparse model. Both approaches are challenging from an optimisation viewpoint due to either the presence of the cardinality constraint or a non-convex constraint on the q-norm. The problem can become even more complex when non-convex distance measures or other real-world constraints are considered. We employ a hybrid heuristic as a flexible tool to tackle both optimisation problems. The empirical analysis on real-world financial data allows to compare the two index tracking approaches. Moreover, we propose a strategy to determine the optimal number of constituents and the corresponding optimal portfolio asset weights

Optimization Heuristics for Determining Internal Rating Grading Scales

Basel II imposes regulatory capital on banks related to the default risk of their credit portfolio. Banks using an internal rating approach compute the regulatory capital from pooled probabilities of default. These pooled probabilities can be calculated by clustering credit borrowers into different buckets and computing the mean PD for each bucket. The clustering problem can become very complex when Basel II regulations and real-world constraints are taken into account. Search heuristics have already proven remarkable performance in tackling this problem. A Threshold Accepting algorithm is proposed, which exploits the inherent discrete nature of the clustering problem. This algorithm is found to outperform alternative methodologies already proposed in the literature, such as standard k-means and Differential Evolution. Besides considering several clustering objectives for a given number of buckets, we extend the analysis further by introducing new methods to determine the optimal number of buckets in which to cluster banks’ clients

Functional Outcomes among Preterm Infants with Intraventricular Hemorrhage

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Occult hepatitis B virus infection: diagnosis, implications and management?

Occult hepatitis B virus (HBV) infection is generally defined as the detection of HBV-DNA in the serum or liver tissue of patients who test negative for hepatitis B surface antigen. In most cases, occult HBV infection is related to low level HBV infection with subdetectable levels of HBsAg and not infection with HBV variants that cannot express S proteins or produce S proteins with aberrant epitopes that are not detected by conventional serological assays. Prevalence of occult HBV infection is related to the overall prevalence of HBV infection in that country, being more common in persons with prior exposure to HBV. Occult HBV infection has been found in a substantial proportion of patients with cirrhosis and hepatocellular carcinoma but other causes of liver disease are frequently present. Future studies should focus on delineating the pathogenic role of occult HBV infection and the basis for failure to detect circulating hepatitis B surface antigen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75344/1/j.1440-1746.2004.03657.x.pd

Las Secuencias Depositacionales del Plioceno-Cuaternario en la Plataforma Submarina adyacente al Litoral del Este Bonaerense

Se describen las características sismoestratigráficas, sedimentológicas y morfológicas del sector de plataforma submarina adyacente al este bonaerense. El trabajo se basa en los resultados obtenidos durante el desarrollo de sucesivos proyectos destinados al estudio de la cubierta sedimentaria del Plioceno-Cuaternario y reciente, utilizando metodologías de relevamiento sísmico de reflexión de media a alta resolución y muestreos de sedimentos. El sector de plataforma estudiado constituye una típica plataforma submarina silicoclástica de margen pasivo, de gran extensión y suave relieve. Su configuración morfológica está caracterizada por relieves aterrazados con una cobertura sedimentaria de depósitos arenosos relicto a palimpsestos que resultaron del retrabajamiento de sistemas costeros de playas, barreras y lagunas litorales durante el retroceso de la línea de costa como consecuencia del ascenso del nivel del mar durante la transgresión postglacial, con una etapa final de remodelado parcial durante el descenso del nivel del mar del Holoceno superior. Se diferencian dos ámbitos, la plataforma interior ("Terraza Rioplatense", entre la línea de costa y los 30/40 m de profundidad) con geoformas ajustadas a la hidrodinámica actual, y la plataforma exterior (entre la isobata de 70 m y el borde exterior de la plataforma en transición al talud), con sedimentos relicto de poca movilidad; en ambas se hallan relieves pre-transgresivos labrados en depósitos marinos y continentales del Plio-Pleistoceno que afloran bajo la cubierta sedimentaria reciente. Un escalón abrupto de 30/40 m de desnivel separa ambas plataformas. La secuencia estratigráfica estudiada está constituida por seis Secuencias Depositacionales (SD 1 a SD 6 de techo a base) que representan paquetes sedimentarios separados por discordancias. La SD 6 constituye la base de la secuencia, y corresponde a depósitos marinos del Mioceno correlacionables con las unidades costeras conocida como "Paranense-Entrerriense-Chapadmalense". La SD 5 son depósitos marinos en transición a continentales equivalentes a la Fm Barranca de los Lobos del litoral marplatense y a la unidad conocida como "Fm Puelches Equivalente" del Plioceno. La SD 4 está caracterizada por sedimentos marinos correspondientes al denominado "Interensenadense" en el litoral bonaerense, de edad aproximada a los 2,41 Ma (Plioceno superior), y se reconocen en ella diversas sismofacies de ambientes marinos, costeros y continentales con una secuencia litológica granodecreciente hacia arriba. La SD 3, marina, tiene la particularidad de tener una distribución saltuaria, a diferencia de las restantes que se extienden de manera uniforme en toda la región, lo que demuestra la ocurrencia, con posterioridad a su depositación, de importantes procesos erosivos probablemente asociados a tectónica y/o glacioeustatismo. La SD 2 representa a los depósitos marinos-costeros formados durante el estadío isotópico 5e (120 ka), que en las llanuras costeras vecinas se lo conoce como "Belgranense", y está constituida por diversas facies entre las que se destacan barreras-lagunas litorales, playas y estuarios. La SD 1 es la cobertura superficial formada durante la transgresión postglacial en ambientes de barreras-lagunas costeras-estuarios. La secuencia integrada por las SD 5 a 1 representa a las transgresiones glacioeustáticas del Plioceno- Cuaternario, con diferentes grados de preservación en la plataforma y el Río de la Plata en virtud de variantes tectónicas y morfológicas. Existe la posibilidad de que no todas las transgresiones marinas ocurridas en la región hayan quedado preservadas en el registro geológico

Molecular detection of Toxoplasma gondii from a naturally infected Alpine chamois (Rupicapra r. rupicapra) from Italian Alps

Background The protozoan Toxoplasma gondii affects many species of domestic (1; 2) and wild (3; 4; 5) warm-blooded animals,raising public health issues related to its zoonotic potential. In this sense wild ungulates may therefore be a source of T. gondii infection for consumers (raw, undercooked meat and fresh sausages) (6; 7; 8) and for hunters and slaughterers through manipulation, evisceration and handling of carcasses (9; 10; 11). Alpine chamois (Rupicapra r. rupicapra) is the most hunted wild ungulate in the Italian Alps with a significant increase of density in the last decades (12); as positiveresultsofserologicaltestingforT. gondii have been reported in the population from the Italian Alps(13; 14) and in southern chamois (Rupicapra pyrenaica) from Spanish Pyrenees (6), we investigated the presence of the protozoan DNA in brain tissues in order to define the receptivity of this species to T. gondii infection and its role in the protozoan lifecycle. Materials and methods During the hunting season 2011, 11 samples of chamois brain tissues were collected in the Lepontine Alps (VB). DNA extraction was performed with the QIAamp DNA Mini Kit (Qiagen, Italy). All the samples were assayed by targeting a 529 bp non-coding region (15), then the positive one was confirmed by a PCR-RFLP assay targeting the 18S small-subunit ribosomal gene of T. gondii, using primers that identify also Neospora caninum and Sarcocystis spp. (16). Results and Discussion T. gondii DNA was detectedin a six-year-old male chamois hunted at an altitudeof 1700 m.a.m.s.l..The subject was in a good body condition and its behaviour was normal;the post-mortem examination did not reveal any systemic macroscopic lesions. The protozoan DNA was detected by both PCR protocols.The PCR-RFLP restriction enzyme analysis of the amplified product confirmed the presence of Toxoplasma gondii, excluding eventual cross-reactions with N. caninum and Sarcocystis spp., closely related to T. gondii. As far as we know, this is the first detection of T. gondii DNA from Alpine chamois. This result confirms the Alpine chamois as intermediate host of T. gondii and demonstrates the protozoan presence in the Alpine ecosystem, even in remote areas. Considering the sporadic presence of linx in the Italian Alps, feral cats are the only definitive hosts of T. gondii, even if transplacental transmissioncan not be excluded. The impact on chamois population dynamics can not properly be evaluated without a better understanding of the epidemiology of infection. In addition, the consumption of raw or undercooked chamois meat could be a possible source of T. gondii infection in humans. In particular, the fact that T. gondii usually affects the host without producing clinical signs (17) could increasethe risk of human infection ascribed to theapparent healthiness of chamois meat. Perspectives and future research priorities Further analysis are needed to define the epidemiology of T.gondii,in particular performing serological study of antibodies against the parasite and the genotyping of the present and future PCR positives samples in order to define (a) prevalence of T. gondii infection in Alpine chamois populations, (b) which parasite strainsare circulating in this alpine ruminant, (c) its pathogenicity and the related zoonosis risk. 6) Acknowledgements We wish to thank all the hunters of the Alpine hunting district (VCO2) in the province of Verbania for their helpduring research in the field, Maria Chiara Cerutti for her useful technical contribution, Donatella Ghidotti and Marzia Marchionni for their helpfulness and collaboration in the lab activities, Ilaria Marangi for her invaluable suggestions that improved the drafting of this manuscript. References 1. Masala G., Porcu R., Madau L., Tanda A., Ibba B., Satta G., Tola S. 2003. Survey of ovine and caprine toxoplasmosis by IFAT and PCR assays in Sardinia, Italy. Veterinary Parasitology, 117: 15-21. 2. Dubey J.P. 1992. Isolation of Toxoplasma gondii from a Naturally Infected Beef Cow. The Journal of Parasitology, 78: 151-153. 3. Jokelainen P., Isomursu M., N\ue4reaho A., Oksanen A. 2011. Natural Toxoplasma gondii infections in european brown hares and mountain hares in Finland: proportional mortality rate, antibody prevalence, and genetic characterization. Journal of Wildlife Diseases, 47: 154-163. 4. Sobrino R., Cabez\uf3n O., Mill\ue1n J., Pab\uf3n M., Arnal M.C., Luco D.F., Gort\ue1zar C., Dubey J.P., Almeria S. 2007. Seroprevalence of Toxoplasma gondii antibodies in wild carnivores from Spain. Veterinary Parasitology, 148: 187-192. 5. B\ue1rtov\ue1 E., Sedl\ue1k K., Liter\ue1k I. 2006. Prevalence of Toxoplasma gondii and Neosporacaninumantibodies in wild boars in the CzechRepublic. Veterinary Parasitology, 142: 150-153. 6. Gauss C.B.L., Dubey J.P., Vidal D., Cabez\uf3n O., Ruiz-Fons F., Vicente J., Marco I., Lavin S., Gort\ue1zar C., Almer\ueda S. 2006. Prevalence of Toxoplasma gondiiantibodies in red deer (Cervuselaphus) and other wild ruminants from Spain. Veterinary parasitology,136: 193-200. 7. Ross R.D., Stec L.A., Werner J.C., Blumenkranz M.S., Glazer L., Williams G.A. 2001. Presumed acquired ocular Toxoplasmosis in deer hunters. Retina, The Journal of Retinal and Vitreous Diseases, 3: 226-229. 8. Dubey J.P. & Beattie C.P. 1988. Toxoplasmosis of Animals and Man.CRC Press, Boca Raton, Florida. 220 pp. 9. Kapperud G., JenumP.A.,Stray-Pedersen B.,Melby K.K., Eskild A., Eng J. 1996. Risk Factors for Toxoplasma gondii Infection in Pregnancy Results of a Prospective Case-Control Study in Norway. American Journal of Epidemiology, 144: 405-412. 10. Dubey J.P. 1994. Toxoplasmosis. Journal of the American Veterinary Medical Association, 205: 1593-1598. 11. McDonald J.C., Gyorkos T.W., Alberton B., MacLean J.D., Richer G., Juranek D. 1990. An Outbreak of Toxoplasmosis in Pregnant Women in Northern Qu\ue9bec. Journal of Infectious Disease, 161: 769-774. 12. Pedrotti L., Dupr\ue8 E., Preatoni D., Toso S. 2001. Banca Dati Ungulati. Status, distribuzione, consistenza, gestione, prelievo venatorio e potenzialit\ue0 delle popolazioni di Ungulati in Italia. Istituto Nazionale per la Fauna Selvatica \u201cAlessandro Ghigi\u201d, 115-129 pp. 13. Gaffuri A.,Giacometti M., Tranquillo V.M., Magnino S.,Cordioli P., Lanfranchi P. 2006. Serosurvey of Roe Deer, Chamois and Domestic Sheep in the CentralItalian Alps. Journal of Wildlife Diseases, 42:685-690. 14. Gennero M.S., Meneguz P.G., MandolaM., MasoeroL., De MeneghiD., RossiL.1993. Indagini sierologiche su ruminanti selvatici in Piemonte. Atti Societa` Italiana delle Scienze Veterinarie, 47: 979-983. 15. Homan W.L., Vercammen M., De Braekeleer J., Verschueren H. 2000. Identification of a 200- to 300-fold repetitive 529 bp DNA fragment in Toxoplasma gondii, and its use for diagnostic and quantitative PCR. International Journal for Parasitology, 30: 69-75. 16. Magnino S., Vigo P.G., Bandi C., Colombo M., De Giuli L., Fabbi M., Genchi C. 1998. PCR diagnosis for Neosporacaninuminfection in aborted bovine foetuses and for Toxoplasma gondii infection in hares and goats in Italy. Pp. 1269-1272. In: Proceedings of the IX International Congress of Parasitology, MakuhariMesse, Chiba, Japan, 24-28 August 1998. 17. Marco I., Velarde R., L\uf3pez-Olvera J.R., Cabez\uf3n O., Pumarola M., Lav\uedn S. 2009. Systemic toxoplasmosis and Gram-negative sepsis in a southern chamois (Rupicaprapyrenaica) from the Pyrenees in northeast Spain. Journal of Veterinary Diagnostic Investigation, 21:244-247

Paleoenvironmental record of the Marine Isotope Stage 2 in the South-bonaerensian outer continental shelf, Argentina: a new contribution to the regional evolution

Se describe la evolución paleoambiental de la plataforma exterior del sureste bonaerense durante la última parte del Estadio Isotópico 2, a partir del estudio de un testigo a 100 m de profundidad cuya secuencia sedimentaria transgresiva grada desde facies fluvio-estuarinas a facies de barreras-lagunas costeras de edad ca. 15 ka cal AP.A core obtained at 100 m water depth in the outer shelf of southeastern Buenos Aires is described. It contains a sedimentary sequence in transgressive facies that records for the first time in the region the evolution of barriers-coastal lagoon environments during the last part of Marine Isotope Stage 2 with an age ca. 15 ka cal AP.Fil: Violante, Roberto Antonio. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Laprida, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; ArgentinaFil: Bressan, Graciela Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; ArgentinaFil: Díaz, Germán Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; ArgentinaFil: Bozzano, Graziella. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Grant, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: García Chapori, Natalia Luz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; ArgentinaFil: Cavallotto, José Luis. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Maidana, Nora Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Cianfagna, Francisco Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Osterrieth, Margarita Luisa. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; ArgentinaFil: Paterlini, C. Marcelo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Costa, Irundo P.. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentin

Linear, Deterministic, and Order-Invariant Initialization Methods for the K-Means Clustering Algorithm

Over the past five decades, k-means has become the clustering algorithm of choice in many application domains primarily due to its simplicity, time/space efficiency, and invariance to the ordering of the data points. Unfortunately, the algorithm's sensitivity to the initial selection of the cluster centers remains to be its most serious drawback. Numerous initialization methods have been proposed to address this drawback. Many of these methods, however, have time complexity superlinear in the number of data points, which makes them impractical for large data sets. On the other hand, linear methods are often random and/or sensitive to the ordering of the data points. These methods are generally unreliable in that the quality of their results is unpredictable. Therefore, it is common practice to perform multiple runs of such methods and take the output of the run that produces the best results. Such a practice, however, greatly increases the computational requirements of the otherwise highly efficient k-means algorithm. In this chapter, we investigate the empirical performance of six linear, deterministic (non-random), and order-invariant k-means initialization methods on a large and diverse collection of data sets from the UCI Machine Learning Repository. The results demonstrate that two relatively unknown hierarchical initialization methods due to Su and Dy outperform the remaining four methods with respect to two objective effectiveness criteria. In addition, a recent method due to Erisoglu et al. performs surprisingly poorly.Comment: 21 pages, 2 figures, 5 tables, Partitional Clustering Algorithms (Springer, 2014). arXiv admin note: substantial text overlap with arXiv:1304.7465, arXiv:1209.196

Chromosome alterations in human hepatocellular carcinomas correlate with aetiology and histological grade – results of an explorative CGH meta-analysis

All available comparative genomic hybridisation (CGH) analyses (n=31, until 12/2003) of human hepatocellular carcinomas (HCCs; n=785) and premalignant dysplastic nodules (DNs; n=30) were compiled and correlated with clinical and histological parameters. The most prominent amplifications of genomic material were present in 1q (57.1%), 8q (46.6%), 6p (22.3%), and 17q (22.2%), while losses were most prevalent in 8p (38%), 16q (35.9%), 4q (34.3%), 17p (32.1%), and 13q (26.2%). Deletions of 4q, 16q, 13q, and 8p positively correlated with hepatitis B virus aetiology, while losses of 8p were more frequently found in hepatitis C virus-negative cases. In poorly differentiated HCCs, 13q and 4q were significantly under-represented. Moreover, gains of 1q were positively correlated with the occurrence of all other high-frequency alterations in HCCs. In DNs, amplifications were most frequently present in 1q and 8q, while deletions occurred in 8p, 17p, 5p, 13q, 14q, and 16q. In conclusion, aetiology and dedifferentiation correlate with specific genomic alterations in human HCCs. Gains of 1q appear to be rather early events that may predispose to further chromosomal abnormalities. Thus, explorative CGH meta-analysis generates novel and testable hypotheses regarding the cause and functional significance of genomic alterations in human HCCs