Luis Ortiz - Academia.edu (original) (raw)

Papers by Luis Ortiz

Proceedings of The National Academy of Sciences, 2007

bleomycin ͉ inflammation

We have investigated a potential role for tumor necrosis factor (TNF)- a and its two receptors (p... more We have investigated a potential role for tumor necrosis factor (TNF)- a and its two receptors (p55 and p75) in lung injury. We used several varieties of mice exposed endotracheally to two fibrogenic agents, sil- ica (0.2 g/kg) and bleomycin (4 U/kg). The lungs were analyzed at 14 and 28 d after exposure to bleomy- cin or silica, respectively, for

Earth and Planetary Science Letters, 1992

The Late Jurassic-Early Cretaceous Alisitos-Teloloapan intra-oceanic arc, which extends along the... more The Late Jurassic-Early Cretaceous Alisitos-Teloloapan intra-oceanic arc, which extends along the Pacific coast of Mexico, is overlain by the extensive thick calc-alkaline Tertiary volcanics of the Sierra Madre Occidental. In central-southern Mexico this arc can be divided in to two major units. Its base, which is mainly exposed in the Guanajuato-Leon area, consists of a volcano-plutonic assemblage refered to as the Guanajuato magmatic sequence. The top consists of pillowed calc-alkaline basalts and andesites overlain and/or interbedded with a thick volcaniclastic sedimentary pile in which lenses of reworked Albian-Aptian reefal limestones are interlayered. The Guanajuato magmatic sequence represents the crustal section of an intra-oceanic nascent island arc and from top to base is made up of: (1) volcaniclastic sedimentary cover, (2) a predominantly pillowed basaltic sequence, (3) a doleritic and basaltic dyke complex, (4) silicic plutonic rocks and salite diorite, (5) Mg-hornblende diorite, (6) layered cumulate gabbros and, (7) ultramafic-mafic cumulates. Plutonic rocks of intermediate to silicic composition are volumetrically abundant. All the rocks have suffered low-grade metamorphism with magmatic textures preserved. Metamorphic textures do not occur. Mg-rich olivine is restricted to the ultramafic cumulates, whereas Ca-rich clinopyroxene is present in all the rock types, although with the exception of the most differentiated silica rich plutonic rocks. The textural relationships and mineral chemistry of the clinopyroxenes and hornblende in the ultramafic cumulates and in the clinopyroxene gabbros point to an origin by igneous accumulation from a tholeiitic parent magma at shallow levels above the mantle-crust boundary.Al-rich basalts and dolerites belong to a low-K tholeiitic suite. The Nb contents, which are abnormaly high for arc tholeiites, are in the range of N-MORB. Such enrichments have been related to an immature stage of the arc development, the mantle wedge being still enriched. This is in agreement with the evidence that the Guanajuato tholeiitic magma represents the earliest products of the Alisitos-Teloloapan arc magmatic activity. The Guanajuato basic rocks and hornblende diorite show similar high εNd ratios which fall in the range of the values of oceanic arcs. The most siliceous plutonic rocks differ from the basic suite by virtue of their slightly lower εNd and higher εSr ratios, which may be explained by an assimilation-fractional crystallization (AFC) process. The siliceous melts differentiated by crystal fractionation from the tholeiitic mantle magma and assimilated material such as metamorphosed oceanic crust and sediments, which form the wall rocks of the magma chamber. The high εSr ratios of the basalts and their feeder dykes are probably related to the polyphase low-grade metamorphism (i.e. hydrothermal oceanic alteration and regional metamorphism) that has affected the uppermost levels of the arc.

Proceedings of The National Academy of Sciences, 2003

Previously we described a reliable method based on immunodepletion for isolating mesenchymal stem... more Previously we described a reliable method based on immunodepletion for isolating mesenchymal stem cells (MSCs) from murine bone marrow and showed that, after intracranial transplantation, the cells migrated throughout forebrain and cerebellum and adopted neural cell fates. Here we systemically administered MSCs purified by immunodepletion from male bleomycin (BLM)-resistant BALB͞c mice into female BLM-sensitive C57BL͞6 recipients and quantified engraftment levels in lung by real-time PCR. Male DNA accounted for 2.21 ؋ 10 ؊5 % of the total lung DNA in control-treated mice but was increased 23-fold (P ‫؍‬ 0.05) in animals exposed to BLM before MSC transplantation. Fluorescence in situ hybridization revealed that engrafted male cells were localized to areas of BLM-induced injury and exhibited an epithelium-like morphology. Moreover, purification of type II epithelial cells from the lungs of transplant recipients resulted in a 3-fold enrichment of male, donor-derived cells as compared with whole lung tissue. MSC administration immediately after exposure to BLM also significantly reduced the degree of BLM-induced inflammation and collagen deposition within lung tissue. Collectively, these studies demonstrate that murine MSCs home to lung in response to injury, adopt an epithelium-like phenotype, and reduce inflammation and collagen deposition in lung tissue of mice challenged with BLM.

Experimental Lung Research, 1998

Bleomycin (BLM) induction of lung fibrosis in mice is an established model to study the mechanism... more Bleomycin (BLM) induction of lung fibrosis in mice is an established model to study the mechanism of pulmonary fibrosis. Cytokine secretion has been implicated as a fundamental component of the lung fibrotic process observed in response to BLM. Among the cytokines implicated in lung fibrosis, Tumor necrosis factor (TNF) alpha has been considered to play a fundamental role. In the present study, we characterized the cellular sources of TNF during BLM-induced lung injury and examined the importance of TNF receptors in this process. To characterize the expression of TNF, we utilized two strains of mice, one sensitive (C57BL/6) and one resistant (BALB/c) to BLM-induced lung injury. Mice received BLM (120 mg/kg total) or saline, as control, by multiple subcutaneous injections. BLM induced the development of inflammation in subpleural areas only in the lungs of BLM-sensitive mice. These subpleural areas were characterized by infiltration of CD68-positive macrophages and increased collagen deposition. BLM enhanced the expression of TNF mRNA in BLM-sensitive, but not in BLM-resistant, mice. In situ hybridization studies localized the expression of TNF in the areas of BLM-induced inflammation in 6% and 27% of macrophages at 14 and 21 days post BLM treatment. In addition to TNF, BLM exposure resulted in the upregulated expression of transforming growth factor (TGF)-beta 1, but not interleukin (IL)-1, mRNA in the lungs of both murine strains at 14 and 21 days. This upregulated expression of TGF-beta 1 mRNA was greater in the lungs of BLM-sensitive mice. In separate experiments, double TNF receptor knockout mice were exposed to BLM. These animals demonstrated an increased expression of TNF, but not TGF-beta 1, mRNA in response to BLM and did not exhibit histologic evidence of lung injury following BLM exposure. In summary, the upregulation of TNF mRNA in macrophages correlated with the appearance of inflammation following BLM exposure and was limited to the BLM-sensitive strain. Furthermore, in addition to the release of the TNF ligand, it appears that the presence of TNF receptors is necessary for the development of BLM-induced lung injury, and signaling through these receptors may contribute to the regulation of the TGF-beta 1 mRNA expression observed in response to bleomycin. These results provide further support for a role of macrophages and TNF in the induction of lung inflammation.

National Conference on Artificial Intelligence, 2000

Sampling has become an important strategy for inference in belief networks. It can also be applie... more Sampling has become an important strategy for inference in belief networks. It can also be applied to the problem of selecting actions in influence diagrams. In this paper, we present methods with probabilistic guarantees of selecting a near-optimal action. We establish bounds on the number of samples required for the traditional method of estimating the utilities of the actions, then go on to extend the traditional method based on ideas from sequential analysis, generating a method requiring fewer samples. Finally, we exploit the intuition that equally good value estimates for each action are not required, to develop a heuristic method that achieves major reductions in required sample size. The heuristic method is validated empirically.

Uncertainty in Artificial Intelligence, 2000

Sampling is an important tool for estimating large, complex sums and integrals over highdimension... more Sampling is an important tool for estimating large, complex sums and integrals over highdimensional spaces. For instance, importance sampling has been used as an alternative to exact methods for inference in belief networks. Ideally, we want to have a sampling distribution that provides optimal-variance estimators. In this paper, we present methods that improve the sampling distribution by systematically adapting it as we obtain information from the samples. We present a stochastic-gradient-descent method for sequentially updating the sampling distribution based on the direct minimization of the variance. We also present other stochastic-gradient-descent methods based on the minimization of typical notions of distance between the current sampling distribution and approximations of the target, optimal distribution. We finally validate and compare the different methods empirically by applying them to the problem of action evaluation in influence diagrams.

Uncertainty in Artificial Intelligence, 1999

Page 1. Accelerating EM: An Empirical Study Luis E. Ortiz £ and Leslie Pack Kaelbling Ý Computer ... more Page 1. Accelerating EM: An Empirical Study Luis E. Ortiz £ and Leslie Pack Kaelbling Ý Computer Science Department, Box 1910 Brown University, Providence, RI 02912 USA leo,lpk @cs.brown.edu Abstract Many applications ...

Uncertainty in Artificial Intelligence, 2001

We consider the problem of approximate belief-state monitoring using particle filtering for the p... more We consider the problem of approximate belief-state monitoring using particle filtering for the purposes of implementing a policy for a partially observable Markov decision process (POMDP). While particle filtering has become a widely used tool in AI for monitoring dynamical systems, rather scant attention has been paid to their use in the context of decision making. Assuming the existence of a value function, we derive error bounds on decision quality associated with filtering using importance sampling. We also describe an adaptive procedure that can be used to dynamically determine the number of samples required to meet specific error bounds. Empirical evidence is offered supporting this technique as a profitable means of directing sampling effort where it is needed to distinguish policies.

Neural Information Processing Systems, 2002

We introduce NashProp, an iterative and local message-passing algorithm for computing Nash equili... more We introduce NashProp, an iterative and local message-passing algorithm for computing Nash equilibria in multi-player games represented by arbitrary undirected graphs. We provide a formal analysis and experimental evidence demonstrating that NashProp performs well on large graphical games with many loops, often converging in just a dozen iterations on graphs with hundreds of nodes. NashProp generalizes the tree algorithm of , and can be viewed as similar in spirit to belief propagation in probabilistic inference, and thus complements the recent work of (Vickrey and Koller 2002), who explored a junction tree approach. Thus, as for probabilistic inference, we have at least two promising general-purpose approaches to equilibria computation in graphs.

Neural Information Processing Systems, 2003

Current Opinion in Pediatrics, 2003

Several epidemiologic studies have shown that intrauterine growth retardation is a risk factor fo... more Several epidemiologic studies have shown that intrauterine growth retardation is a risk factor for the development of cardiovascular disease in later life. In this review, we discuss these epidemiologic studies and animal models that have been developed to investigate the pathophysiology of this phenomenon. We discuss data suggesting that intrauterine growth retardation leads to fetal exposure to maternal glucocorticoids. In addition, we present other data showing that fetal exposure of glucocorticoids during specific times of fetal development results in focal and segmental glomerulosclerosis, a reduced number of nephrons, hypertension, and diabetes. These studies suggest that at critical times during fetal development fetal injury programs the development of cardiovascular disease and diabetes in later life.

CVPR 2011, 2011

We propose an agent-based behavioral model of pedestrians to improve tracking performance in real... more We propose an agent-based behavioral model of pedestrians to improve tracking performance in realistic scenarios. In this model, we view pedestrians as decision-making agents who consider a plethora of personal, social, and environmental factors to decide where to go next. We formulate prediction of pedestrian behavior as an energy minimization on this model. Two of our main contributions are simple,

Lecture Notes in Computer Science, 2004

Page 1. Graphical Economics Sham M. Kakade, Michael Kearns, and Luis E. Ortiz Department of Compu... more Page 1. Graphical Economics Sham M. Kakade, Michael Kearns, and Luis E. Ortiz Department of Computer and Information Science University of Pennsylvania, Philadelphia, PA 19104 {skakade,mkearns,leortiz}@linc.cis.upenn.edu Abstract. ...

Computational Learning Theory, 2004

We introduce a graph-theoretic generalization of classical Arrow-Debreu economics, in which an un... more We introduce a graph-theoretic generalization of classical Arrow-Debreu economics, in which an undirected graph specifies which consumers or economies are permitted to engage in direct trade, and the graph topology may give rise to local variations in the prices of commodities. Our main technical contributions are: (1) a general existence theorem for graphical equilibria, which require local markets to clear; (2) an improved algorithm for computing approximate equilibria in standard (non-graphical) economies, which generalizes the algorithm of Deng et al. [2002] to non-linear utility functions; (3) an algorithm for computing equilibria in the graphical setting, which runs in time polynomial in the number of consumers in the special but important case in which the graph is a tree (again permitting non-linear utility functions). We also highlight many interesting learning problems that arise in our model, and relate them to learning in standard game theory and economics, graphical games, and graphical models for probabilistic inference.

Neural Information Processing Systems, 2004

There is a long history of research in economics on mathematical models for exchange mar-kets, an... more There is a long history of research in economics on mathematical models for exchange mar-kets, and the existence and properties of their equilibria. The work of Arrow and Debreu [1954], who established equilibrium existence in a very general commodities exchange ...

ACM Conference on Electronic Commerce, 2003

We examine correlated equilibria in the recently introduced formalism of graphical games, a succi... more We examine correlated equilibria in the recently introduced formalism of graphical games, a succinct representation for multiplayer games. We establish a natural and powerful relationship between the graphical structure of a multiplayer game and a certain Markov network representing distributions over joint actions. Our first main result establishes that this Markov network succinctly represents all correlated equilibria of the graphical game up to expected payoff equivalence. Our second main result provides a general algorithm for computing correlated equilibria in a graphical game based on its associated Markov network. For a special class of graphical games that includes trees, this algorithm runs in time polynomial in the graphical game representation (which is polynomial in the number of players and exponential in the graph degree).

IEEE Expert / IEEE Intelligent Systems, 2003

The Penn-Lehman automated trading project is a broad investigation of algorithms and strategies f... more The Penn-Lehman automated trading project is a broad investigation of algorithms and strategies for automated trading in financial markets. The PLAT project's centerpiece is the Penn exchange simulator (PXS), a software simulator for automated stock trading that merges automated client orders for shares with real-world, real-time order data. PXS automatically computes client profits and losses, volumes traded, simulator and external prices, and other quantities of interest. To test the effectiveness of PXS and of various trading strategies, we've held three formal competitions between automated clients.

Perfiles Educativos, 2014

Hypertension, 2003

Dexamethasone is frequently administered to the developing fetus to accelerate pulmonary developm... more Dexamethasone is frequently administered to the developing fetus to accelerate pulmonary development. The purpose of the present study was to determine if prenatal dexamethasone programmed a progressive increase in blood pressure and renal injury in rats. Pregnant rats were given either vehicle or 2 daily intraperitoneal injections of dexamethasone (0.2 mg/kg body weight) on gestational days 11 and 12, 13 and 14, 15 and 16, 17 and 18, or 19 and 20. Offspring of rats administered dexamethasone on days 15 and 16 gestation had a 20% reduction in glomerular number compared with control at 6 to 9 months of age (22 527Ϯ509 versus 28 050Ϯ561, PϽ0.05), which was comparable to the percent reduction in glomeruli measured at 3 weeks of age. Six-to 9-month old rats receiving prenatal dexamethasone on days 17 and 18 of gestation had a 17% reduction in glomeruli (23 380Ϯ587) compared with control rats (PϽ0.05). Male rats that received prenatal dexamethasone on days 15 and 16, 17 and 18, and 13 and 14 of gestation had elevated blood pressures at 6 months of age; the latter group did not have a reduction in glomerular number. Adult rats given dexamethasone on days 15 and 16 of gestation had more glomeruli with glomerulosclerosis than control rats. This study shows that prenatal dexamethasone in rats results in a reduction in glomerular number, glomerulosclerosis, and hypertension when administered at specific points during gestation. Hypertension was observed in animals that had a reduction in glomeruli as well as in a group that did not have a reduction in glomerular number, suggesting that a reduction in glomerular number is not the sole cause for the development of hypertension. (Hypertension. 2003;41:328-334.)