Hector Perez - Academia.edu (original) (raw)

Papers by Hector Perez

Digestive Diseases and Sciences, 2004

To compare H. pylori infection prevalence and gastric mucosa damage in HIV-infected and non-HIV-i... more To compare H. pylori infection prevalence and gastric mucosa damage in HIV-infected and non-HIV-infected patients, gastric biopsies were systematically taken in 209 individuals who underwent upper Gl endoscopy (102 HIV-infected and 107 non-HIV-infected). H. pylori was found in 42 (41.1%) HIV-infected patients and in 53 (49.5%) non-HIV patients (P=0.22, χ2 = 1.47, NS). In HIV-positive patients infected with H. pylori the mean CD4 count was higher than in HIV-positive patients without H. pylori (364 and 228 cells/mm3, respectively; P = 0.0001). H. pylori gastritis was more severe in the HIV-positive group (χ2 = 15.02, P = 0.0001). The frequency of H. pylori in gastric mucosa in HIV-infected and non-HIV patients was similar. HIV-infected patients with H. pylori had a higher mean CD4 count than HIV-infected individuals without H. pylori. Gastric lesions associated with H. pylori were more severe in the HIV-positive population.

Automatica, 2003

This article addresses the optimal (minimum-input-energy) output-transition problem for linear sy... more This article addresses the optimal (minimum-input-energy) output-transition problem for linear systems. The goal is to transfer the output from an initial value y(t) = y (for all time t 6 t i ) to a ÿnal output value y(t) = y (for all time t ¿ t f ). Previous methods solve this output-transition problem by transforming it into a state-transition problem; the initial and ÿnal states (x(t i ); x(t f ), respectively) are chosen and a minimum-energy state-to-state transition problem is solved. However, the choice of the initial and ÿnal states can be ad hoc and the resulting output-transition cost (input energy) may not be minimal. The contribution of this article is the solution of the optimal output-transition problem. An example system with elastic dynamics is studied to illustrate the proposed method. Simulation results are presented that show substantial reduction of transition costs with the use of the proposed method when compared to the use of minimum-energy state-to-state transitions. ?

IEEE Transactions on Control Systems Technology, 2002

Inversion-based approach finds an input that exactly tracks a desired output trajectory-the metho... more Inversion-based approach finds an input that exactly tracks a desired output trajectory-the method has been recently extended to nonlinear nonminimum phase systems using stable-inversion techniques. Exact-output tracking inputs can be found by the stable-inversion method provided the system can be maintained near (local to) an equilibrium point of the system. However, inversion for the nonlocal case is more challenging because inverse solutions may not exist, for example, when the equilibrium point (operating point) is changed. Such changes in operating points are necessary in process control applications, for example, during startups, shutdowns, and grade transitions. Nonlocal transfers of a system from one operating point to another operating point along prespecified output trajectories are studied in this article for the Van de Vusse example, which is a benchmark problem in nonlinear nonminimum-phase process-control.

Journal of Dynamic Systems Measurement and Control-transactions of The Asme, 2004

This article addresses the optimal (minimal input energy) design of scan trajectories, which is i... more This article addresses the optimal (minimal input energy) design of scan trajectories, which is important in applications such as the imaging and manipulation of nano-scale surface phenomena using scanning tunneling microscopes (STM), MEMS-based micro-scanners, quick-return ...

IEEE Transactions on Signal Processing, 1991

Absfruef-A new adaptive filter (ADF) structure is proposed for applications in which large order ... more Absfruef-A new adaptive filter (ADF) structure is proposed for applications in which large order ADF's are required. It is based on modeling the impulse response of the system to be indentified as a linear combination of a set of discrete orthogonal functions. Computer simulations using actual acoustio echo path impulse responses show that the proposed ADF structure has better convergence performance than FIR transversal ADP when they are required to identify systems with long impulse responses.

Electronics Letters, 1988

Plant Journal, 1999

Pro®lin in Phaseolus vulgaris is encoded by two genes (only one expressed in root nodules) but mu... more Pro®lin in Phaseolus vulgaris is encoded by two genes (only one expressed in root nodules) but multiple isoforms are generated in vivo by phosphorylation on tyrosine residues Summary Actin-binding proteins such as pro®lins participate in the restructuration of the actin cytoskeleton in plant cells. Pro®lins are ubiquitous actin-, polyproline-, and inositol phospholipid-binding proteins, which in plants are encoded by multigene families. By 2D-PAGE and immunoblotting, we detected as much as ®ve pro®lin isoforms in crude extracts from nodules of Phaseolus vulgaris. However, by immunoprecipitation and gel electrophoresis of in vitro translation products from nodule RNA, only the most basic isoform of those found in nodule extracts, was detected. Furthermore, a bean pro®lin cDNA probe hybridised to genomic DNA digested with different restriction enzymes, showed either a single or two bands. These data indicate that pro®lin in P. vulgaris is encoded by only two genes. In root nodules only one gene is expressed, and a single pro®lin transcript gives rise to multiple pro®lin isoforms by post-translational modi®cations of the protein. By in vivo 32 P-labelling and immunoprecipitation with both, antipro®lin and antiphosphotyrosine-speci®c antibodies, we found that pro®lin is phosphorylated on tyrosine residues. Since chemical (TLC) and immunological analyses, as well as plant tyrosine phosphatase (AtPTP1) treatments of pro®lin indicated that tyrosine residues were phosphorylated, we concluded that tyrosine kinases must exist in plants. This ®nding will focus research on tyrosine kinases/tyrosine phosphatases that could participate in novel regulatory functions/ pathways, involving not only this multifunctional cytoskeletal protein, but other plant proteins.

The response of the actin cytoskeleton to nodulation (Nod) factors secreted by Rhizobium etli has... more The response of the actin cytoskeleton to nodulation (Nod) factors secreted by Rhizobium etli has been studied in living root hairs of bean (Phaseolus vulgaris) that were microinjected with fluorescein isothiocyanate-phalloidin. In untreated control cells or cells treated with the inactive chitin oligomer, the actin cytoskeleton was organized into long bundles that were oriented parallel to the long axis of the root hair and extended into the apical zone. Upon exposure to R. etli Nod factors, the filamentous actin became fragmented, as indicated by the appearance of prominent masses of diffuse fluorescence in the apical region of the root hair. These changes in the actin cytoskeleton were rapid, observed as soon as 5 to 10 min after application of the Nod factors. It was interesting that the filamentous actin partially recovered in the continued presence of the Nod factor: by 1 h, long bundles had reformed. However, these cells still contained a significant amount of diffuse fluorescence in the apical zone and in the nuclear area, presumably indicating the presence of short actin filaments. These results indicate that Nod factors alter the organization of actin microfilaments in root hair cells, and this could be a prelude for the formation of infection threads.