138 research outputs found
Multi-asset minority games
We study analytically and numerically Minority Games in which agents may invest in different assets (or markets), considering both the canonical and the grand-canonical versions. We find that the likelihood of agents trading in a given asset depends on the relative amount of information available in that market. More specifically, in the canonical game players play preferentially in the stock with less information. The same holds in the grand canonical game when agents have positive incentives to trade, whereas when agents payoff are solely related to their speculative ability they display a larger propensity to invest in the information-rich asset. Furthermore, in this model one finds a globally predictable phase with broken ergodicity
How does informational heterogeneity affect the quality of forecasts?
We investigate a toy model of inductive interacting agents aiming to forecast
a continuous, exogenous random variable E. Private information on E is spread
heterogeneously across agents. Herding turns out to be the preferred
forecasting mechanism when heterogeneity is maximal. However in such conditions
aggregating information efficiently is hard even in the presence of learning,
as the herding ratio rises significantly above the efficient-market expectation
of 1 and remarkably close to the empirically observed values. We also study how
different parameters (interaction range, learning rate, cost of information and
score memory) may affect this scenario and improve efficiency in the hard
phase.Comment: 11 pages, 5 figures, updated version (to appear in Physica A
On the strategy frequency problem in batch Minority Games
Ergodic stationary states of Minority Games with S strategies per agent can
be characterised in terms of the asymptotic probabilities with which
an agent uses of his strategies. We propose here a simple and general
method to calculate these quantities in batch canonical and grand-canonical
models. Known analytic theories are easily recovered as limiting cases and, as
a further application, the strategy frequency problem for the batch
grand-canonical Minority Game with S=2 is solved. The generalization of these
ideas to multi-asset models is also presented. Though similarly based on
response function techniques, our approach is alternative to the one recently
employed by Shayeghi and Coolen for canonical batch Minority Games with
arbitrary number of strategies.Comment: 17 page
Multi-asset minority games
We study analytically and numerically Minority Games in which agents may invest in different assets (or markets), considering both the canonical and the grand-canonical versions. We find that the likelihood of agents trading in a given asset depends on the relative amount of information available in that market. More specifically, in the canonical game players play preferentially in the stock with less information. The same holds in the grand canonical game when agents have positive incentives to trade, whereas when agents payoff are solely related to their speculative ability they display a larger propensity to invest in the information-rich asset. Furthermore, in this model one finds a globally predictable phase with broken ergodicity
Flux distribution in metabolic networks close to optimal biomass production
We study a statistical model describing the steady state distribution of the
fluxes in a metabolic network. The resulting model on continuous variables can
be solved by the cavity method. In particular analytical tractability is
possible solving the cavity equation over an ensemble of networks with the same
degree distribution of the real metabolic network. The flux distribution that
optimizes production of biomass has a fat tail with a power-law exponent
independent on the structural properties of the underling network. These
results are in complete agreement with the Flux-Balance-Analysis outcome of the
same system and in qualitative agreement with the experimental results.Comment: (4 pages,2 figures
New Thoughts on Pediatric Genetic Obesity: Pathogenesis, Clinical Characteristics and Treatment Approach
New Thoughts on Pediatric Genetic Obesity: Pathogenesis, Clinical Characteristics and Treatment Approach
Historically, some genetic syndromes and monogenic forms of obesity have been identified by clinical features and by sequencing candidate genes in patients with severe obesity. The phenotypic expression of genetic factors involved in obesity is variable, thereby allowing to distinguish several clinical pictures of obesity. Monogenic obesity is described as rare and severe earlyâonset obesity with abnormal feeding behavior and endocrine disorders. Many of the findings emerged from studying families who displayed a classical Mendelian pattern of inheritance. On the contrary, patients with syndromic obesity show a various degree of intellectual disability, different dysmorphic features, and organâspecific abnormalities. But to date, not all involved genes have been identified so far. New diagnostic tools, such as genomeâwide studies, array CGH, and wholeâexome sequencing, have highlighted more complex models of inheritance, and even more candidate genes were identified. This increase of knowledge may provide insights into the mechanisms involved in the regulation of body weight and finally lead to specific treatments. In these patients, hyperphagia is often a primary phenotypic component. Substantial gaps in understanding the molecular basis of inherited hyperphagia syndromes are present today with a lack of mechanistic targets that can serve as a basis for pharmacologic and behavioral treatments. We have evaluated retrospectively the literature data on weight, body mass index (BMI), clinical features, treatments, and treatment response in pediatric patients with forms of genetic obesity. However, this chapter provides an updated picture of emerging knowledge outlined by the more comprehensive genetic approaches, trying to outline more candidate genes for these forms of genetic obesity. Relevant papers will be identified through systematic searches of the PubMed, EMBASE and Cochrane databases. All published studies in the English language concerning these disorders will be evaluated. Keywords in the literature search will be entered in all combinations. Searches will be augmented by manually reviewing the reference lists of all original articles and all systematic review articles, with each study being evaluated for inclusion
Metabolomic Profiling and Antioxidant Activity of Fruits Representing Diverse Apple and Pear Cultivars
The false fruits of apple (Malus domestica) and pear (Pyrus communis) are consumed all over the world, contributing to the dietary intake of health-promoting antioxidant phytochemicals. For example, polyphenols confer many beneficial effects (according to their chemical structure, bioavailability, and absorption efficiency in the gut) and the consumption of polyphenol-rich apple and pear fruits may therefore reduce the risk of some diseases. However, the content of such molecules is highly dependent on the specific fruit cultivar. To examine this metabolic diversity in detail, we used metabolomic analysis (NMR and HPLC-DAD/MS) to profile the metabolome of six apple and five pear cultivars. We also determined the antioxidant capacity of the extracts (FRAP assay) and correlated this with the metabolomic composition and abundance of specific metabolites. We observed the cultivar-specific accumulation of sugars, amino acids, malic acid, and various polyphenols, which was also related to the growing season for some cultivars. We found that the ancient Italian apple Pom Prussian was enriched for chlorogenic acid as well as more characteristic polyphenols (phloretin derivatives), the pear cultivar Abate Fetel was low in sucrose, and both cultivars displayed high in vitro antioxidant activity. These cultivars may, therefore, be particularly attractive to health-conscious consumers
Identifying essential genes in E. coli from a metabolic optimization principle
Understanding the organization of reaction fluxes in cellular metabolism from
the stoichiometry and the topology of the underlying biochemical network is a
central issue in systems biology. In this task, it is important to devise
reasonable approximation schemes that rely on the stoichiometric data only,
because full-scale kinetic approaches are computationally affordable only for
small networks (e.g. red blood cells, about 50 reactions). Methods commonly
employed are based on finding the stationary flux configurations that satisfy
mass-balance conditions for metabolites, often coupling them to local
optimization rules (e.g. maximization of biomass production) to reduce the size
of the solution space to a single point. Such methods have been widely applied
and have proven able to reproduce experimental findings for relatively simple
organisms in specific conditions. Here we define and study a constraint-based
model of cellular metabolism where neither mass balance nor flux stationarity
are postulated, and where the relevant flux configurations optimize the global
growth of the system. In the case of E. coli, steady flux states are recovered
as solutions, though mass-balance conditions are violated for some metabolites,
implying a non-zero net production of the latter. Such solutions furthermore
turn out to provide the correct statistics of fluxes for the bacterium E. coli
in different environments and compare well with the available experimental
evidence on individual fluxes. Conserved metabolic pools play a key role in
determining growth rate and flux variability. Finally, we are able to connect
phenomenological gene essentiality with `frozen' fluxes (i.e. fluxes with
smaller allowed variability) in E. coli metabolism.Comment: 9 pages, to appear in PNAS, see
http://www.pnas.org/content/early/2009/02/05/0813229106.abstract for the
early editio
Retrospective evaluation of metformin and/or metformin plus a new polysaccharide complex in treating severe hyperinsulinism and insulin resistance in obese children and adolescents with metabolic syndrome
Background: Pharmacological treatment of obesity and glucose-insulin metabolism disorders in children may be more difficult than in adults. Thus, we evaluate the effects of metformin in comparison with metformin plus a polysaccharide complex (Policaptil Gel RetardÂź, PGR) on body weight and metabolic parameters in obese children and adolescents with metabolic syndrome (MetS). Patients and methods: We retrospectively collected 129 children and adolescents (67 girls, 62 boys; median age 12.6 years) treated for a minimum of two years with metformin and low glycemic index (LGI) diet. Of these, 71 patients were treated with metformin plus PGR after at least 12 months of metformin alone. To minimize the confounding effect of the LGI on auxological and metabolic parameters, the patients were compared with age-, sex-, and BMI-matched control group with obesity and MetS (51 subjects; 24 males, 27 females) treated only with a LGI diet. Assessments included lipids, glucose and insulin (fasting and after oral glucose tolerance test) concentrations. The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), Matsuda, insulinogenic and disposition indices were calculated. Results: Metformin treatment led to a significant reduction in BMI SDS (p < 0.0001), with a significant difference in ÎBMI SDS between patients and controls (p < 0.0001). Moreover, metformin treated patients showed a reduction in HOMA-IR (p < 0.0001), HbA1c levels (p < 0.0001) and a significant increase in Matsuda index (p < 0.0001) in respect to the reduction discovered in controls (p < 0.05). Moreover, in contrast to the group treated with metformin alone and controls, patients treated with metformin plus PGR showed a further reduction in BMI SDS (p < 0.0001), HOMA-IR (p < 0.0001), HbA1c (p < 0.0001), total, HDL and LDL cholesterol (p < 0.0001), as well as an increase in Matsuda (p < 0.0001), disposition (p < 0.005) and insulinogenic (respectively, p < 0.05 and p < 0.0001) indices. Conclusions: Metformin appears to show short-term efficacy in reducing BMI, adiposity and glucose and insulin parameters in obese children and adolescents with MetS. However, PGR added to metformin may be useful to potentiate weight loss and to improve glucose-insulin metabolism and adiposity parameters in these patients
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