Papers by Luis Fernado Lopez
Theoretical biology & medical modelling, Jan 12, 2017
National or local laws, norms or regulations (sometimes and in some countries) require medical pr... more National or local laws, norms or regulations (sometimes and in some countries) require medical providers to report notifiable diseases to public health authorities. Reporting, however, is almost always incomplete. This is due to a variety of reasons, ranging from not recognizing the diseased to failures in the technical or administrative steps leading to the final official register in the disease notification system. The reported fraction varies from 9 to 99% and is strongly associated with the disease being reported. In this paper we propose a method to approximately estimate the full prevalence (and any other variable or parameter related to transmission intensity) of infectious diseases. The model assumes incomplete notification of incidence and allows the estimation of the non-notified number of infections and it is illustrated by the case of hepatitis C in Brazil. The method has the advantage that it can be corrected iteratively by comparing its findings with empirical results....
Clinics (São Paulo, Brazil), Aug 1, 2016
Dengue cases range from asymptomatic to severe, eventually leading to hospitalization and death. ... more Dengue cases range from asymptomatic to severe, eventually leading to hospitalization and death. Timely and appropriate management is critical to reduce morbidity. Since 1980, dengue has spread throughout Brazil, affecting an increasing number of individuals. This paper describes age and regional differences in dengue's clinical presentation and associated risk of hospitalization based on more than 5 million cases reported to the Brazilian Ministry of Health from 2000-2014. We performed a retrospective analysis of ∼5,450,000 dengue cases, relating clinical manifestations and the risk of hospitalization to age, gender, previous infection by dengue, dengue virus serotype, years of formal education, delay to first attendance and the occurrence of dengue during outbreaks and in different Brazilian regions. Complicated forms of dengue occurred more frequently among those younger than 10 years (3.12% vs 1.92%) and those with dengue virus 2 infection (7.65% vs 2.42%), with a delay to f...
BMC infectious diseases, Jan 29, 2016
Rio de Janeiro in Brazil will host the Summer Olympic Games in 2016. About 400,000 non-immune for... more Rio de Janeiro in Brazil will host the Summer Olympic Games in 2016. About 400,000 non-immune foreign tourists are expected to attend the games. As Brazil is the country with the highest number of dengue cases worldwide, concern about the risk of dengue for travelers is justified. A mathematical model to calculate the risk of developing dengue for foreign tourists attending the Olympic Games in Rio de Janeiro in 2016 is proposed. A system of differential equation models the spread of dengue amongst the resident population and a stochastic approximation is used to assess the risk to tourists. Historical reported dengue time series in Rio de Janeiro for the years 2000-2015 is used to find out the time dependent force of infection, which is then used to estimate the potential risks to a large tourist cohort. The worst outbreak of dengue occurred in 2012 and this and the other years in the history of Dengue in Rio are used to discuss potential risks to tourists amongst visitors to the f...
2015 IFIP/IEEE International Symposium on Integrated Network Management (IM), 2015
Operating unprotected network links for international collaboration between research and educatio... more Operating unprotected network links for international collaboration between research and education communities, subject to a high-availability production service requirement, is challenging. Provisioning circuits, maintaining a loop-free network topology, and configuring multipath redundancy to provide high availability are complex processes, which involve extensive coordination between, and manual configuration operations carried out by, multiple network operators, resulting in high operations costs. Moreover, network-oriented research applications increasingly require the capability to program network functions to satisfy particular requirements, such as high tolerance, low delay, end-to-end visibility, etc. We describe a solution, based on Software-Defined Networking (SDN), which significantly lowers the operations costs by automating most network operations and reducing coordination efforts between network operators. The design of the network, before and after SDN was deployed, is discussed. For each network function migrated to SDN, a comparative analysis is provided with metrics, first to represent real measurements before and after each SDN deployment scenario, and second, to describe findings of reduced operations costs.
BMC Medicine, 2015
Background: The endgame of polio eradication is hampered by the international spread of polioviru... more Background: The endgame of polio eradication is hampered by the international spread of poliovirus via travelers. In response to ongoing importations of poliovirus into polio-free countries, on 5 May 2014, WHO's Director-General declared the international spread of wild poliovirus a public health emergency of international concern. Our objective was to develop a mathematical model to estimate the international spread of polio infections. Methods: Our model took into account polio endemicity in polio-infected countries, population size, polio immunization coverage rates, infectious period, the asymptomatic-to-symptomatic ratio, and also the probability of a traveler being infectious at the time of travel. We applied our model to three scenarios: (1) number of exportations of both symptomatic and asymptomatic polio infections out of currently polio-infected countries, (2) the risk of spread of poliovirus to Saudi Arabia via Hajj pilgrims, and (3) the importation risk of poliovirus into India. Results: Our model estimated 665 polio exportations (>99 % of which were asymptomatic) from nine polio-infected countries in 2014, of which 78.3 % originated from Pakistan. Our model also estimated 21 importations of poliovirus into Saudi Arabia via Hajj pilgrims and 20 poliovirus infections imported to India in the same year. Conclusion: The extent of importations of asymptomatic and symptomatic polio infections is substantial. For countries that are vulnerable to polio outbreaks due to poor national polio immunization coverage rates, our newly developed model may help guide policy-makers to decide whether imposing an entry requirement in terms of proof of vaccination against polio would be justified.
Lecture Notes in Computer Science, 2006
This paper introduces a novel unstructured P2P system able to adapt its overlay network topology ... more This paper introduces a novel unstructured P2P system able to adapt its overlay network topology to the load conditions. The adaptation is performed by means of a mechanism which is run by the nodes in the network in an autonomous manner using only local information, so no global coordinator is needed. The aim of this adaptation is to build an efficient topology for the resource discovery mechanism performed via random walks. We present the basis of the adaptation mechanism, along with some simulation results obtained under different conditions. These results show that this system is efficient and robust, even in front of directed attacks.
Lecture Notes in Computer Science, 2005
Physical Review E, 2002
In the context of complex network systems, we model social networks with the property that there ... more In the context of complex network systems, we model social networks with the property that there is certain degradation of the information flowing through the network. We analyze different kinds of networks, from regular lattices to random graphs. We define an average coordination degree for the network, which can be associated with a certain notion of efficiency. Assuming that there is a limit to the information a person may handle, we show that there exists a close relationship between the structure of the network and its maximum size.
Theory of Computing Systems, 2007
In this paper we start the study of generalizing the Adversarial Queueing Theory (aqt) model towa... more In this paper we start the study of generalizing the Adversarial Queueing Theory (aqt) model towards a continuous scenario in which the usually assumed synchronicity of the evolution is not required anymore. We consider a model, named continuous AQT (caqt), in which packets can have arbitrary lengths, and the network links may have different speeds (or bandwidths) and propagation delays. We show that, in such a general model, having bounded queues implies bounded endto-end packet delays and vice versa. From the network point of view, we show that networks with directed acyclic topologies are universally stable, i.e., stable independently of the protocols and the traffic patterns used in it, and that this even holds for traffic patterns that make links to be fully loaded. Concerning packet scheduling protocols, we show that the well-known lis, sis, ftg and nfs protocols remain universally stable in our model. We also show that the caqt model is strictly stronger than the aqt model by presenting scheduling policies that are unstable under the former while they are universally stable under the latter.
The Astrophysical Journal, 2010
We use high spatial resolution (∼7 pc) CARMA observations to derive detailed properties for 8 gia... more We use high spatial resolution (∼7 pc) CARMA observations to derive detailed properties for 8 giant molecular clouds (GMCs) at a galactocentric radius corresponding to approximately two CO scale lengths, or ∼ 0.5 optical radii (r 25), in the Local Group spiral galaxy M33. At this radius, molecular gas fraction, dust-togas ratio and metallicity are much lower than in the inner part of M33 or in a typical spiral galaxy. This allows us to probe the impact of environment on GMC properties by comparing our measurements to previous data from the inner disk of M33, the Milky Way and other nearby galaxies. The outer disk clouds roughly fall on the size-linewidth relation defined by extragalactic GMCs, but are slightly displaced from the luminosity-virial mass relation in the sense of having high CO luminosity compared to the inferred virial mass. This implies a different CO-to-H 2 conversion factor, which is on average a factor of two lower than the inner disk and the extragalactic average. We attribute this to significantly higher measured brightness temperatures of the outer disk clouds compared to the ancillary sample of GMCs, which is likely an effect of enhanced radiation levels due to massive star formation in the vicinity of our target field. Apart from brightness temperature, the properties we determine for the outer disk GMCs in M33 do not differ significantly from those of our comparison sample. In particular, the combined sample of inner and outer disk M33 clouds covers roughly the same range in size, linewidth, virial mass and CO luminosity than the sample of Milky Way GMCs. When compared to the inner disk clouds in M33, however, we find even the brightest outer disk clouds to be smaller than most of their inner disk counterparts. This may be due to incomplete sampling or a potentially steeper cloud mass function at larger radii.
The Astrophysical Journal, 2011
We report the discovery of a powerful molecular wind from the nucleus of the non-interacting near... more We report the discovery of a powerful molecular wind from the nucleus of the non-interacting nearby S0 field galaxy NGC 1266. The single-dish CO profile exhibits emission to ±400 km s −1 and requires a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrallyconcentrated molecular component with a mass of 1.1 × 10 9 M ⊙ and a molecular outflow with a molecular mass of ≈ 2.4 × 10 7 M ⊙. The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1×10 8 M ⊙ within a radius of ≈ 60 pc. This compact molecular nucleus has a surface density of ≈ 2.7 × 10 4 M ⊙ pc −2 , more than two orders of magnitude larger than that of giant molecular clouds in the disk of the Milky Way, and it appears to sit on the Kennicutt-Schmidt relation despite its extreme kinematics and energetic activity. We interpret this nucleus as a disk that confines the outflowing wind. A mass outflow rate of ≈ 13 M ⊙ yr −1 leads to a depletion timescale of 85 Myr. The star formation in NGC 1266 is insufficient to drive the outflow, and thus it is likely driven by the active galactic nucleus (AGN). The concentration of the majority of the molecular gas in the central 100 pc requires an extraordinary loss of angular momentum, but no obvious companion or interacting galaxy is present to enable the transfer. NGC 1266 is the first known outflowing molecular system that does not show any evidence of a recent interaction.
Phytoparasitica, 1996
Encapsulation of eggs of Metaphycus stanleyi Compere by the pyriform scale, Protopulvinaria pyrif... more Encapsulation of eggs of Metaphycus stanleyi Compere by the pyriform scale, Protopulvinaria pyriformis (Cockerell), under both greenhouse and field conditions, was found to occur almost all year round. However, encapsulation rates varied considerably during the different seasons; they were correlated with the ambient temperatures and were affected by the host plant. Encapsulation rates (i) in scales infesting avocado in the Bet Dagan orchard, were lowest during October to May (0-11%) and highest during June to August (54-75%); (ii) in scales infesting Hedera helix and Scheffiera arboricola under greenhouse conditions, were lowest during December to May (6-17%) and highest during July to September (78-100%). Under greenhouse conditions, encapsulation rates did not differ between scales grown on H. helix and on S. arboricola, but were significantly lower in scales grown on avocado. Encapsulation rates of eggs of M. stanleyi and/or Metaphycus swirskii Annecke and Mynhardt in scales infesting avocado in the Miqwe Yisra'el orchard, were lowest during December to February (1-10%) and highest during July to August (49-75%). Encapsulation of eggs of M. stanleyi and/or Metaphycus galbus Annecke (42%) was also recorded in P pyriformis on avocado from Spain. The high rates of encapsulation of Metaphycus spp. eggs by P pyriformis during the summer, may interfere with efficient biological control of the pest.
Physical Review E, 2012
The critical behavior of self-assembled rigid rods on a square lattice was recently reinvestigate... more The critical behavior of self-assembled rigid rods on a square lattice was recently reinvestigated by Almarza et al. [Phys. Rev. E 82, 061117 (2010)]. Based on the Binder cumulants and the value of the critical exponent of the correlation length, the authors found that the isotropic-nematic phase transition occurring in the system is in the two-dimensional Ising universality class. This conclusion contrasts with that of a previous study [López et al., Phys. Rev. E 80, 040105 (R) (2009)] which indicates that the transition at intermediate density belongs to the q = 1 Potts universality class. Almarza et al. attributed the discrepancy to the use of the density as the control parameter by López et al. The present work shows that this suggestion is not sufficient, and that the discrepancy arises solely from the use of different statistical ensembles. Finally, the necessity of making corrections to the scaling functions in the canonical ensemble is discussed.
Physical Review E, 2005
Most studies in complex networks assume that once a link is created between two nodes it is never... more Most studies in complex networks assume that once a link is created between two nodes it is never deleted. However, there is a recent interest towards systems where links can be rapidly rewired. An important issue in that type of networks is to discover the topology that, given a search algorithm, optimizes the search process. In this paper, we present a system model that, depending on the current network congestion, makes nodes to establish link connections so that the resulting topologies tend to a starlike when congestion is small and to randomlike topologies when congestion becomes relevant. Those topologies have been shown to be optimal in the above-mentioned conditions. Such a model can be easily implemented in practice and therefore, may be relevant in areas as the topology management of peer-to-peer networks.
Physica A: Statistical Mechanics and its Applications, 2001
This paper analyzes a model for the competition dynamics of web sites in the Internet, based on t... more This paper analyzes a model for the competition dynamics of web sites in the Internet, based on the Lotka-Volterra competition equations. This model shows the well known appearance of a winner-take-all characteristic and is based in the nonvalidity of traditional o er and demand equilibrium theory of these kinds of markets. From the stability analysis of the model, we establish a series of rules which are useful for deÿning strategies in the Internet market. One of the most important results that emerge from this simple model is the appearance of some unexpected phenomena related to the collaboration and competition between sites.
Microelectronics Journal, 2002
Silicon die surface temperature can be used to monitor the health state of digital and analogue i... more Silicon die surface temperature can be used to monitor the health state of digital and analogue integrated circuits (IC). In the present paper, four different sensing techniques: scanning thermal microscope, laser reflectometer, laser interferometer and electronic built-in differential temperature sensors are used to measure the temperature at the surface of the same IC containing heat sources (hot spots) that behave as faulty digital gates. The goal of the paper is to describe the techniques as well as to present the performances of these sensing methods for the detection and localisation of hot spots in an IC.
Medical Hypotheses, 2005
In this work we propose a simple mathematical model for the analysis of the impact of control mea... more In this work we propose a simple mathematical model for the analysis of the impact of control measures against an emerging infection, namely, the severe acute respiratory syndrome (SARS). The model provides a testable hypothesis by considering a dynamical equation for the contact parameter, which drops exponentially with time, simulating control measures. We discuss the role of modelling in public health and we analyse the distinction between forecasting and projection models as assessing tools for the estimation of the impact of intervention strategies. The model is applied to the communities of Hong Kong and Toronto (Canada) and it mimics those epidemics with fairly good accuracy. The estimated values for the basic reproduction number, R 0 , were 1.2 for Hong Kong and 1.32 for Toronto (Canada). The model projects that, in the absence of control, the final number of cases would be 320,000 in Hong Kong and 36,900 in Toronto (Canada). In contrast, with control measures, which reduce the contact rate to about 25% of its initial value, the expected final number of cases is reduced to 1778 in Hong Kong and 226 in Toronto (Canada). Although SARS can be a devastating infection, early recognition, prompt isolation, and appropriate precaution measures, can be very effective to limit its spread.
Computational and Mathematical Methods in Medicine, 2013
To determine the maximum equilibrium prevalence of mosquito-borne microparasitic infections, this... more To determine the maximum equilibrium prevalence of mosquito-borne microparasitic infections, this paper proposes a general model for vector-borne infections which is flexible enough to comprise the dynamics of a great number of the known diseases transmitted by arthropods. From equilibrium analysis, we determined the number of infected vectors as an explicit function of the model’s parameters and the prevalence of infection in the hosts. From the analysis, it is also possible to derive the basic reproduction number and the equilibrium force of infection as a function of those parameters and variables. From the force of infection, we were able to conclude that, depending on the disease’s structure and the model’s parameters, there is a maximum value of equilibrium prevalence for each of the mosquito-borne microparasitic infections. The analysis is exemplified by the cases of malaria and dengue fever. With the values of the parameters chosen to illustrate those calculations, the maxim...
The American Journal of Human Genetics, 2008
Muscle coenzyme Q 10 (CoQ 10 or ubiquinone) deficiency has been identified in more than 20 patien... more Muscle coenzyme Q 10 (CoQ 10 or ubiquinone) deficiency has been identified in more than 20 patients with presumed autosomal-recessive ataxia. However, mutations in genes required for CoQ 10 biosynthetic pathway have been identified only in patients with infantileonset multisystemic diseases or isolated nephropathy. Our SNP-based genome-wide scan in a large consanguineous family revealed a locus for autosomal-recessive ataxia at chromosome 1q41. The causative mutation is a homozygous splice-site mutation in the aarF-domain-containing kinase 3 gene (ADCK3). Five additional mutations in ADCK3 were found in three patients with sporadic ataxia, including one known to have CoQ 10 deficiency in muscle. All of the patients have childhood-onset cerebellar ataxia with slow progression, and three of six have mildly elevated lactate levels. ADCK3 is a mitochondrial protein homologous to the yeast COQ8 and the bacterial UbiB proteins, which are required for CoQ biosynthesis. Three out of four patients tested showed a low endogenous pool of CoQ 10 in their fibroblasts or lymphoblasts, and two out of three patients showed impaired ubiquinone synthesis, strongly suggesting that ADCK3 is also involved in CoQ 10 biosynthesis. The deleterious nature of the three identified missense changes was confirmed by the introduction of them at the corresponding positions of the yeast COQ8 gene. Finally, a phylogenetic analysis shows that ADCK3 belongs to the family of atypical kinases, which includes phosphoinositide and choline kinases, suggesting that ADCK3 plays an indirect regulatory role in ubiquinone biosynthesis possibly as part of a feedback loop that regulates ATP production.
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Papers by Luis Fernado Lopez