632 research outputs found
- A COMPUTATIONAL APPROACH TO THE FUNDAMENTAL THEOREM OF ASSET PRICING IN A SINGLE-PERIOD MARKET.
In this paper we provide a new approach to the Fundamental Theorem of As-set Pricing. The proofof this result is usually based on Projection (Separation) Theorems and is far more intuitive. Ourapproach follow the relation between the projection problem an equivalent least squares problem.More precisely, we will use and iterative procedure in order to obtain solutions of a bounded leastsquare problem. This solutions will give, under some conditions, either the state price vector orthe arbitrage opportunity of the problem under consideration.Asset Pricing; Arbitrage; Mathematical Finance
Learning about knowledge: A complex network approach
This article describes an approach to modeling knowledge acquisition in terms
of walks along complex networks. Each subset of knowledge is represented as a
node, and relations between such knowledge are expressed as edges. Two types of
edges are considered, corresponding to free and conditional transitions. The
latter case implies that a node can only be reached after visiting previously a
set of nodes (the required conditions). The process of knowledge acquisition
can then be simulated by considering the number of nodes visited as a single
agent moves along the network, starting from its lowest layer. It is shown that
hierarchical networks, i.e. networks composed of successive interconnected
layers, arise naturally as a consequence of compositions of the prerequisite
relationships between the nodes. In order to avoid deadlocks, i.e. unreachable
nodes, the subnetwork in each layer is assumed to be a connected component.
Several configurations of such hierarchical knowledge networks are simulated
and the performance of the moving agent quantified in terms of the percentage
of visited nodes after each movement. The Barab\'asi-Albert and random models
are considered for the layer and interconnecting subnetworks. Although all
subnetworks in each realization have the same number of nodes, several
interconnectivities, defined by the average node degree of the interconnection
networks, have been considered. Two visiting strategies are investigated:
random choice among the existing edges and preferential choice to so far
untracked edges. A series of interesting results are obtained, including the
identification of a series of plateaux of knowledge stagnation in the case of
the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure
Ofertas de suplementos múltiplos para tourinhos na fase de recria, em pastagens durante o periodo da seca: desempenho produtivo.
The current importance of Leishmaniasis in Spain
Se pasa revisión al estado actual de los principales elementos epidemiológicos de las
leishmaniosis en España: parásito, reservorio canino, flebotomo vector, y hombre, poniendo de manifiesto la importancia sanitaria, social y económica de la enfermedad. Se termina recogiendo datos recientes sobre el diagnóstico y tratamiento de la enfermedad.A revision is made of the current state of the principal epidemiological elements of
leishmaniasis in Spain (the parasite, the canine population, the sandflies vector, and
humans), while stating the sanitary, social and economic significance of the disease.
Finally, recent information is given regarding the diagnosis and treatment of the disease
Ofertas de suplementos múltiplos para tourinhos Nelore na fase de recria em pastagens durante o período da seca: desempenho produtivo e características nutricionais.
Avaliaram-se o desempenho produtivo e as características nutricionais em tourinhos Nelore em fase de recria, não-castrados, recebendo diferentes ofertas de suplementos em pastagem de Brachiaria decumbens, de julho a setembro de 2006. A área foi dividida em cinco piquetes de 2,0 ha, com disponibilidade média de matéria seca (MS) e matéria seca potencialmente digestível (MSpd) de 3,88 e 2,22 t/ha, respectivamente. Foram utilizados 30 bezerros com peso e idade iniciais médios de 230,0 ± 6,14 kg e 8,5 ± 0,18 meses, em delineamento inteiramente casualizado contendo cinco tratamentos: quatro ofertas de suplementos em comparação a mistura mineral (MM). Foram avaliados a MM (60 g/animal) e suplementos múltiplos, fornecidos diariamente nas quantidades de 0,5; 1,0; 1,5 e 2,0 kg/animal para suprir 300 g/dia de PB. Os animais responderam ao uso de suplementos múltiplos, ganhando mais peso (88,72%) e apresentaram maiores níveis séricos de N-ureia (19,95 vs. 9,66) em comparação àqueles que receberam mistura mineral. Os animais sob suplementação apresentaram maiores consumos de MS, MO, EE, FDN, CNF e NDT e esses consumos aumentaram com os níveis de oferta de suplemento. A suplementação aumentou o coeficiente de digestão da maioria das variáveis avaliadas, independentemente do nível de suplemento fornecido. Os níveis mais moderados (0,5 kg) de suplementos múltiplos podem ser fornecidos aos tourinhos em fase de recria durante o período da seca para estimular o consumo de pasto, porém a máxima produção microbiana é obtida com oferta de 1,34 kg de suplemento. As melhores respostas de desempenho e características nutricionais podem ser obtidas com o fornecimento diário de suplemento em níveis de 0,5 a 1,34 kg/animal
Collaboration in sensor network research: an in-depth longitudinal analysis of assortative mixing patterns
Many investigations of scientific collaboration are based on statistical
analyses of large networks constructed from bibliographic repositories. These
investigations often rely on a wealth of bibliographic data, but very little or
no other information about the individuals in the network, and thus, fail to
illustrate the broader social and academic landscape in which collaboration
takes place. In this article, we perform an in-depth longitudinal analysis of a
relatively small network of scientific collaboration (N = 291) constructed from
the bibliographic record of a research center involved in the development and
application of sensor network and wireless technologies. We perform a
preliminary analysis of selected structural properties of the network,
computing its range, configuration and topology. We then support our
preliminary statistical analysis with an in-depth temporal investigation of the
assortative mixing of selected node characteristics, unveiling the researchers'
propensity to collaborate preferentially with others with a similar academic
profile. Our qualitative analysis of mixing patterns offers clues as to the
nature of the scientific community being modeled in relation to its
organizational, disciplinary, institutional, and international arrangements of
collaboration.Comment: Scientometrics (In press
Order statistics of the trapping problem
When a large number N of independent diffusing particles are placed upon a
site of a d-dimensional Euclidean lattice randomly occupied by a concentration
c of traps, what is the m-th moment of the time t_{j,N} elapsed
until the first j are trapped? An exact answer is given in terms of the
probability Phi_M(t) that no particle of an initial set of M=N, N-1,..., N-j
particles is trapped by time t. The Rosenstock approximation is used to
evaluate Phi_M(t), and it is found that for a large range of trap
concentracions the m-th moment of t_{j,N} goes as x^{-m} and its variance as
x^{-2}, x being ln^{2/d} (1-c) ln N. A rigorous asymptotic expression (dominant
and two corrective terms) is given for for the one-dimensional
lattice.Comment: 11 pages, 7 figures, to be published in Phys. Rev.
A 40-year evaluation of drivers of African rainforest change
Background: Tropical forests are repositories of much of the world’s biodiversity and are critical for mitigation of climate change. Yet, the drivers of forest dynamics are poorly understood. This is in large part due to the lack of long-term data on forest change and changes in drivers. Methodology: We quantify changes in tree abundance, diversity, and stand structure along transects first enumerated in 1978 and resampled 2019 in Kibale National Park, Uganda. We tested five predictions. First, based on the purported role of seed dispersal and herbivory and our quantification of changes in the abundance of frugivores and herbivores, we tested two predictions of how faunal change could have influenced forest composition. Second, based on an evaluation of life history strategies, we tested two predictions concerning how the forest could have changed following disturbance that happened prior to written history. Finally, based on a 50-year climate record, we evaluate the possible influence of climate change on forest dynamics. Results: More trees were present on the assessed transects in 2019 (508) than in 1978 (436), species richness remained similar, but diversity declined as the number of dominant species increased. Rainfall increased by only 3 mm over the 50 years but this had not significant effect on forest changes measured here. Annual average monthly maximum temperature increased significantly by 1.05 °C over 50 years. The abundance of frugivorous and folivorous primates and elephants increased over the 50 years of monitoring. Neither the prediction that an increase in abundance of seed dispersing frugivores increases the abundance of their preferred fruiting tree species, nor that as an increase in folivore abundance causes a decline in their preferred species were supported. As predicted, light-demanding species decreased in abundance while shade-tolerant species increased as expected from Kibale being disturbed prior to historical records. Finally, while temperature increased over the 50 years, we found no means to predict a priori how individual species would respond. Conclusions: Our study revealed subtle changes in the tree community over 40 years, sizable increases in primate numbers, a substantial increase in the elephant population and an increase in local temperature. Yet, a clear picture of what set of interactions impact the change in the tree community remains elusive. Our data on tree life-history strategies and frugivore/herbivore foraging preferences suggest that trees species are under opposing pressures
Future research demands of the United European Gastroenterology (UEG) and its member societies
AIMS: The purpose of this study was to initiate and stimulate collaborative research efforts to support United European Gastroenterology Federation (UEG) member societies facilitating digestive health research in European on the one hand and, on the other hand, to increase EU-funded digestive health research by providing evidence and advice to funding bodies on priority areas. The UEG Research Committee initiated a survey of the current and future research interests of each individual UEG ordinary member society (specialist societies). METHODS: A questionnaire was sent by mail to 17 UEG ordinary member societies asking them to specify research demands related to the most urgent medical need including basic science research, translational research, clinical research, patient management research and research on disease prevention, in an open fashion but with limited word count. RESULTS: The responses from 13 societies were analysed in a semi-quantitative and in a qualitative way, and were clustered into five domains with two aspects each that were consented and shared between three and seven of the responding 13 societies. These clusters resemble topics such as ‘Hot topics’ (e.g. life-style, nutrition, microbial-host interaction), Biomarkers (genetic profiling, gut-brain interaction), Advanced technology (artificial intelligence, personalised medicine), Global research tools (bio-banking, EU trials), and Medical training (education, prevention). CONCLUSION: The generated topic list allows both collaboration between individual specialist societies as well as initiating and fostering future research calls at the EU level and beyond when approaching stakeholders
A New Approach to Analyzing Patterns of Collaboration in Co-authorship Networks - Mesoscopic Analysis and Interpretation
This paper focuses on methods to study patterns of collaboration in
co-authorship networks at the mesoscopic level. We combine qualitative methods
(participant interviews) with quantitative methods (network analysis) and
demonstrate the application and value of our approach in a case study comparing
three research fields in chemistry. A mesoscopic level of analysis means that
in addition to the basic analytic unit of the individual researcher as node in
a co-author network, we base our analysis on the observed modular structure of
co-author networks. We interpret the clustering of authors into groups as
bibliometric footprints of the basic collective units of knowledge production
in a research specialty. We find two types of coauthor-linking patterns between
author clusters that we interpret as representing two different forms of
cooperative behavior, transfer-type connections due to career migrations or
one-off services rendered, and stronger, dedicated inter-group collaboration.
Hence the generic coauthor network of a research specialty can be understood as
the overlay of two distinct types of cooperative networks between groups of
authors publishing in a research specialty. We show how our analytic approach
exposes field specific differences in the social organization of research.Comment: An earlier version of the paper was presented at ISSI 2009, 14-17
July, Rio de Janeiro, Brazil. Revised version accepted on 2 April 2010 for
publication in Scientometrics. Removed part on node-role connectivity profile
analysis after finding error in calculation and deciding to postpone
analysis
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