Carlos Alcantara Estrada - Academia.edu (original) (raw)

Papers by Carlos Alcantara Estrada

2009 IEEE International Conference on Robotics and Automation, 2009

In this paper we describe an algorithm to compute cycle constraints that can be used in many grap... more In this paper we describe an algorithm to compute cycle constraints that can be used in many graph-based SLAM algorithms; we exemplify it in Hierarchical SLAM. Our algorithm incrementally computes the minimum cycle basis of constraints from which any other cycle can be derived. Cycles in this basis are local and of minimum length, so that the associated cycle constraints have less linearization problems. This also permits to construct regional maps, that is, it makes possible efficient and accurate intermediate mapping levels between local maps and the whole global map. We have extended our algorithm to the multi-robot case. We have tested our methodology using the Victoria Park data set with satisfactory results.

Journal of general internal medicine, Nov 25, 2016

Journal of General Internal Medicine, 2015

Journal of Multidisciplinary Healthcare, 2015

Background: Mammography screening for women under the age of 50 is controversial. Groups such as ... more Background: Mammography screening for women under the age of 50 is controversial. Groups such as the US Preventive Services Task Force recommend counseling women 40-49 years of age about mammography risks and benefits in order to incorporate the individual patient's values in decisions regarding screening. We assessed the impact of a brief educational intervention on the knowledge and attitudes of clinicians regarding breast cancer screening. Methods: The educational intervention included a review of the risks and benefits of screening, individual risk assessment, and counseling methods. Sessions were led by a physician expert in breast cancer screening. Participants were physicians and nurses in 13 US Department of Veterans Affairs primary care clinics in Alabama. Outcomes were as follows: 1) knowledge assessment of mammogram screening recommendations; 2) counseling practices on the risks and benefits of screening; and 3) comfort level with counseling about screening. Outcomes were assessed by survey before and after the intervention. Results: After the intervention, significant changes in attitudes about breast cancer screening were seen. There was a decrease in the percentage of participants who reported that they would screen all women ages 40-49 years (82% before the intervention, 9% afterward). There was an increase in the percentage of participants who reported that they would wait until the patient was 50 years old before beginning to screen (12% before the intervention, 38% afterward). More participants (5% before, 53% after; P,0.001) said that they would discuss the patient's preferences. Attitudes favoring discussion of screening benefits increased, though not significantly, from 94% to 99% (P=0.076). Attitudes favoring discussion of screening risks increased from 34% to 90% (P,0.001). The comfort level with discussing benefits increased from a mean of 3.8 to a mean of 4.5 (P,0.001); the comfort level with discussing screening risks increased from 2.7 to 4.3 (P,0.001); and the comfort level with discussing cancer risks and screening preferences with patients increased from 3.2 to 4.3 (P,0.001). (The comfort levels measurements were assessed by using a Likert scale, for which 1= not comfortable and 5= very comfortable.) Conclusion: Most clinicians in the US Department of Veterans Affairs ambulatory practices in Alabama reported that they routinely discuss mammography benefits but not potential harms with patients. An educational intervention detailing recommendations and counseling methods affected the knowledge and attitudes about breast cancer screening. Participants expressed greater likelihood of discussing screening options in the future.

Southern Medical Journal, 2006

Cirrhosis is the 12th leading cause of death in the United States. Individuals with cirrhosis are... more Cirrhosis is the 12th leading cause of death in the United States. Individuals with cirrhosis are at risk for many potential complications. Complications can be managed or detected early with proper outpatient management. The most lethal of these complications is bleeding esophageal varices. All patients with cirrhosis should be screened for the presence of varices and treated when indicated. The most common complication seen in these patients is ascites. Ascites can be treated with dietary modifications and a diuretic regimen. Other potential complications include spontaneous bacterial peritonitis, hepatocellular carcinoma, hepatic encephalopathy, hepatorenal syndrome, and hepatopulmonary syndrome. The outpatient management of these complications will be discussed in this paper, along with the use of vaccinations, educating patients about the avoidance of hepatotoxic drugs, and when to refer a patient for liver transplant.

The Receptors

Rheumatoid arthritis (RA) affects 1% of the U.S. population, or 3 million people. RA is a chronic... more Rheumatoid arthritis (RA) affects 1% of the U.S. population, or 3 million people. RA is a chronic inflammatory disease characterized by synovial inflammation and hyperplasia, neovascularization, and progressive destruction of cartilage and bone. The cause(s) of RA remains poorly defined, but it is thought that both genetic and environmental factors, including molecular mimicry and host responses against cross-reactive antigens, lead to the development of autoimmune responses involving the joints. The goal of this chapter is to provide an overview of the contribution of members of the chemokine system to the immunopathogenesis of RA. This is of high clinical relevance because of the burgeoning interest in the use of chemokine and chemokine-receptor blockers in the treatment of a variety of inflammatory, autoimmune, and infectious disorders, including RA.

Proceedings of SPE Asia Pacific Conference on Integrated Modelling for Asset Management, 2000

Copyright 2000, Society of Petroleum Engineers Inc. This paper was prepared for presentation at t... more Copyright 2000, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 2000 SPE Asia Pacific Conference on Integrated Modelling for Asset Management held in Yokohama, Japan, 2526 April 2000. This paper was selected for presentation by an ...

Surface Science, 1991

The adsorption and decomposition of methanol on copper overlayers on the Rh(100) surface have bee... more The adsorption and decomposition of methanol on copper overlayers on the Rh(100) surface have been studied using thermal desorption mass spectrometry (TDMS) and high-resolution electron energy loss spectroscopy (HREELS). The reaction scheme of methanol on this model bimetallic catalyst is similar to that on the clean Rh(lO0) surface, but with a number of important differences. First, the presence of a monolayer or more of copper on the Rh(100) surface greatly inhibits methanol decomposition and also reduces the binding energy of molecularly adsorbed methanol. That portion of the methanol monolayer that desorbs reversibly desorbs near 200 K on a Rh(100) surface witb a pseudomorphic copper monolayer and at-380 K when two or more monolayers of copper are present, compared with approximately 210 K on clean Rh(100). Second, formation of methoxy via OH bond cleavage of the adsorbed methanol occurs on the copper overlayer as on the clean surface. but to a reduced extent. Compared with methoxy formed on clean ~(I~), which decomposes completely by 320 K, methoxy formed on the copper overlayers is substantially more stable. On a pseudorno~~~ copper monolayer, the methoxy is stable up to-370 K; when two or more monolayers of copper are present, the methoxy decomposition is complete only near 400 K. ,Unlike the case of methoxy on clean Rh(lOO), decomposition of methoxy on the copper overlayers is accompanied by formaldehyde evolution. Third, the methoxy on the copper overlayers exhibits a metal-oxygen stretching frequency that is substantially reduced compared with the frequency of this mode on clean Rh(100). These observations are discussed in relation to the chemistry of methanol on various copper surfaces, and in terms of the electronic and structural effects which may lead to such changes.

Renewable Energy, 1995

The calculation of the incident solar radiation falling upon tubular collectors presents difficul... more The calculation of the incident solar radiation falling upon tubular collectors presents difficulties which do not exist when this is carried out for flat plate collectors. Due to their cylindrical shape, the solar incident radiation on their surface is a function of angle and time, This paper presents experimental results which were obtained by means of a device specially designed in order to measure the distribution of such radiation. The device's sensor element (a photodiode) was characterised, calibrated and subsequently used to measure the angular distribution of radiation incident on the inside surface of the inner tube of an evacuated solar collector. It was found that the experimentally measured distribution agrees with that obtained by the ray-tracing method which appears in the literature.

Journal of Molecular Medicine, 2005

CCR2 has been widely considered as a potential therapeutic target for autoimmune disease, particu... more CCR2 has been widely considered as a potential therapeutic target for autoimmune disease, particularly rheumatoid arthritis, and various CCR2 blocking agents have been developed, some of which have entered clinical trials. In this review, we examine the relevant information regarding the role of CCR2, and to a lesser extent of the closely related chemokine receptor CCR5, in the immunopathogenesis of collagen-induced arthritis, an animal model of rheumatoid arthritis. Experimental evidence showing that CIA is accelerated and exacerbated when CCR2 is genetically inactivated (knockout mice) or blocked with specific antibodies warrant additional investigations before the relevance of the findings in rodent models can be applied to human patients with RA.

Journal of Irrigation and Drainage Engineering, 2009

GESTAR is an advanced computational hydraulic software tool specially adapted for the design, pla... more GESTAR is an advanced computational hydraulic software tool specially adapted for the design, planning, and management of pressurized irrigation networks. A summary is given of the most significant characteristics of GESTAR. The hydraulic solver for quasi-steady scenarios uses specific strategies and incorporates several new features that improve the algorithms for pipe network computation, overcoming some of the problems that arise when attempting to apply drinking water software, using the gradient method, to irrigation systems. It is shown that the gradient method is a nodal method variant, where flow rates are relaxed using head loss formula exponents. Although relaxation produces a damping effect on instabilities, it is still unable to solve some of the numerical problems common to the nodal methods. In this contribution the results of the research on computational strategies capable of dealing with low resistance elements, hydrant modelling, multiple regulation valves, numerous emitters, and pumps with complex curves are presented, obtaining accurate results even in conditions where other software fails to converge. GESTAR incorporates all these computational techniques, achieving a high convergence rate and robustness. Furthermore, GESTAR's solver algorithm was easily adapted to incorporate inverse analysis options for optimum network control and parameter calibration. Illustrative examples are provided, documenting the improved numerical techniques and examples of GESTAR's performance in comparison with EPANET2, a widely used gradient methodbased hydraulic solver.

Journal of Hydrology, 2007

Nutrient fluxes in rainfall and throughfall were measured weekly in a mature subtropical wet fore... more Nutrient fluxes in rainfall and throughfall were measured weekly in a mature subtropical wet forest in NE Puerto Rico over a 15-year period that included the effects of 10 named tropical storms, several prolonged dry periods, and volcanic activity in the region. Mean annual rainfall and throughfall were 3482 and 2131 mm yr À1 , respectively. Average annual rainfall and throughfall fluxes of K, Ca, Mg, Cl, Na, and SO 4-S were similar but somewhat larger than those reported for most tropical forests. Rainfall inputs of nitrogen were comparatively low and reflect the relative isolation of the airshed. More constituents had seasonal differences in rainfall fluxes (6 out of 12) than throughfall fluxes (4 out of 12) and all volume weighted throughfall enrichment ratios calculated for the 15-year period were greater than one. However, median weekly enrichment ratios were less than 1 for sea salts and dissolved organic carbon, between 1 and 2 for Mg, Ca, SiO 2 and SO 4-S, and greater than 10 for NH 4-N, PO 4-P, and K. Droughts tended to reduce enrichment ratios of cations and sea-salts, but increased enrichment ratios of NH 4-N, PO 4-P, and K. In the weeks following hurricanes and tropical storms, relative throughfall tended to be higher and enrichment ratios tended to be lower. Saharan dust and the activity of Caribbean volcanoes can also be detected in the time series. Nevertheless, the impacts of particular events are variable and modified by the magnitude of the event, the preand post-event rainfall, and the time since the previous event. Rainfall, throughfall, rainfall pH, and rainfall fluxes of seven constituents had decreasing trends over the 15-year period. However, these decreases were small, less than inter-annual and annual varia

Journal of General Internal Medicine, 2000

To determine if the American College of Cardiology (ACC) cardiac monitoring guidelines accurately... more To determine if the American College of Cardiology (ACC) cardiac monitoring guidelines accurately stratify patients according to their risks for developing clinically significant arrhythmias in non-intensive-care settings, we conducted a prospective cohort study of 2,240 consecutive patients admitted to a non-intensive-care telemetry unit over 7 months. Sixty-one percent of patients were assigned to ACC class I (telemetry indicated in most patients), 38% to class II (telemetry indicated in some), and 1% to class III (telemetry not indicated). Arrhythmias were detected in 13.5% of the class I patients, 40.7% of the class II patients, and 12% of the class III patients (p Ͻ .001). Telemetry detected an arrhythmia resulting in transfer to an intensive care unit in 0.4% of the class I patients, 1.6% of the class II patients, and none of the class III patients (p ϭ .006). Telemetry led to a change in management for 3.4% of the class I patients, 12.7% of the class II patients, and 4% of the class III patients (p Ͻ .001). When patients with chest pain as the reason for admission were moved from class I to class II and patients with arrhythmias as the reason for admission were moved from class II to class I, more arrhythmias and more clinically significant arrhythmias occurred in class I patients and the trends from class I to class III were more consistent with the purpose of the guidelines. These findings indicate that when the ACC guidelines are reexamined, consideration should be given to changing them so they are more useful in non-intensive-care settings.

Journal of General Internal Medicine, 2008

BACKGROUND: Residents demonstrate scholarly activity by presenting posters at academic meetings. ... more BACKGROUND: Residents demonstrate scholarly activity by presenting posters at academic meetings. Although recommendations from national organizations are available, evidence identifying which components are most important is not. OBJECTIVE: To develop and test an evaluation tool to measure the quality of case report posters and identify the specific components most in need of improvement. DESIGN: Faculty evaluators reviewed case report posters and provided on-site feedback to presenters at poster sessions of four annual academic general internal medicine meetings. A newly developed ten-item evaluation form measured poster quality for specific components of content, discussion, and format (5-point Likert scale, 1 = lowest, 5 = highest). Main outcome measure(s): Evaluation tool performance, including Cronbach alpha and inter-rater reliability, overall poster scores, differences across meetings and evaluators and specific components of the posters most in need of improvement. RESULTS: Forty-five evaluators from 20 medical institutions reviewed 347 posters. Cronbach's alpha of the evaluation form was 0.84 and inter-rater reliability, Spearman's rho 0.49 (p<0.001). The median score was 4.1 (Q1-Q3, 3.7-4.6)(Q1=25th, Q3=75th percentile). The national meeting median score was higher than the regional meetings (4.4 vs, 4.0, P<0.001). We found no difference in faculty scores. The following areas were identified as most needing improvement: clearly state learning objectives, tie conclusions to learning objectives, and use appropriate amount of words. CONCLUSIONS: Our evaluation tool provides empirical data to guide trainees as they prepare posters for presentation which may improve poster quality and enhance their scholarly productivity.

Journal of Continuing Education in the Health Professions, 2009

Introduction-Physician use of the Internet for practice improvement has increased dramatically ov... more Introduction-Physician use of the Internet for practice improvement has increased dramatically over the last decade, but research shows that many physicians choose not to participate. The current study investigated the association of specific physician characteristics with enrollment rates and intensity of participation in a specific Internet-delivered educational intervention to improve care to post-myocardial infarction (MI) patients. Methods-Primary-care physicians were recruited for participation in a randomized controlled trial designed to compare effectiveness of an intervention Web site versus a control Web site in the management of adult chronic disease. Physicians were informed that the intervention focused on ambulatory post-myocardial infarction patients. Physician characteristics were obtained from a commercial vendor with data merged from the American Medical Association and Alabama State Licensing Board. Enrollment and Web use were tracked electronically.

Journal of Clinical Gastroenterology, 1990

Infectious Diseases in Obstetrics and Gynecology, 2000

Objective: To review critically and to summarize the evidence of diagnostic tests and culture med... more Objective: To review critically and to summarize the evidence of diagnostic tests and culture media for the diagnosis of Trichomonas vaginitis. Methods: We performed a systematic review of literature indexed in MEDLINE of studies that used Trichomonas culture as the reference standard (9,882 patients, 35 studies). Level I studies (5,047 patients, 13 studies) fulfilled at least two of three criteria: 1) consecutive patients were evaluated prospectively, 2) decision to culture was not influenced by test results, and 3) there was independent and blind comparison to culture. Results: The sensitivity of the polymerase chain reaction technique (PCR) was 95% (95% CI 91% to 99%), and the specificity was 98% (95% CI 96% to 100%). One study was classified as Level I evidence (52 patients). The sensitivity of the enzyme-linked immunosorbent assay was 82% (95% CI 74% to 90%), and the specificity was 73% (95% CI 35% to 100%). The sensitivity of the direct fluorescence antibody was 85% (95% CI 79% to 90%), and the specificity was 99% (95% CI 98% to 100%). Sensitivities of culture media were 95% for Diamond's, 96% for Hollander, and 95% for CPLM. Conclusions: The sensitivity and specificity of tests to diagnose trichomoniasis vary widely. Infect.

IEEE Transactions on Robotics, 2005

In this paper we present a hierarchical mapping method that allows to obtain accurate metric maps... more In this paper we present a hierarchical mapping method that allows to obtain accurate metric maps of large environments in real time. The lower (or local) map level is composed of a set of local maps that are guaranteed to be statistically independent. The upper (or global) level is an adjacency graph whose arcs are labelled with the relative location between local maps. An estimation of these relative locations is maintained at this level in a relative stochastic map. We propose a close to optimal loop closing method that, while maintaining independence at the local level, imposes consistency at the global level at a computational cost linear with the size of the loop. Experimental results demonstrate the efficiency and precision of the proposed method by mapping the Ada Byron building at our campus. We also analyze, using simulations, the precision and convergence of our method for larger loops.

Diabetologia, 2011

Aims/hypothesis Chemokines and their receptors such as chemokine (C-C motif) receptor 2 (CCR2) ma... more Aims/hypothesis Chemokines and their receptors such as chemokine (C-C motif) receptor 2 (CCR2) may contribute to the pathogenesis of the metabolic syndrome via their effects on inflammatory monocytes. Increased accumulation of CCR2-driven inflammatory monocytes in epididymal fat pads is thought to favour the development of insulin resistance. Ultimately, the resulting hyperglycaemia and dyslipidaemia contribute to development of the metabolic syndrome complications such as cardiovascular disease and diabetic nephropathy. Our goal was to elucidate the role of CCR2 and inflammatory monocytes in a mouse model that resembles the human metabolic syndrome. Methods We generated a model of the metabolic syndrome by backcrossing KKAy + with Apoe −/− mice (KKAy + Apoe −/−) and studied the role of CCR2 in this model system. Results KKAy + Apoe −/− mice were characterised by the presence of obesity, insulin resistance, dyslipidaemia and increased systemic inflammation. This model also manifested two complications of the metabolic syndrome: atherosclerosis and diabetic nephropathy. Inactivation of Ccr2 in KKAy + Apoe −/− mice protected against the metabolic syndrome, as well as atherosclerosis and diabetic nephropathy. This protective phenotype was associated with a reduced number of inflammatory monocytes in the liver and muscle, but not in the epididymal fat pads; circulating levels of adipokines such as leptin, resistin and adiponectin were also not reduced. Interestingly, the proportion of inflammatory monocytes in the liver, pancreas and muscle, but not in the epididymal fat pads, correlated significantly with peripheral glucose levels. Conclusions/interpretation CCR2-driven inflammatory monocyte accumulation in the liver and muscle may be a critical pathogenic factor in the development of the metabolic syndrome.

Circulation Research, 2007

Nuclear factor kappa B (NF-κB) participates in hypertension-induced vascular and target-organ dam... more Nuclear factor kappa B (NF-κB) participates in hypertension-induced vascular and target-organ damage. We tested whether or not endothelial cell–specific NF-κB suppression would be ameliorative. We generated Cre/lox transgenic mice with endothelial cell–restricted NF-κB super-repressor IκBαΔN (Tie-1-ΔN mice) overexpression. We confirmed cell-specific IκBαΔN expression and reduced NF-κB activity after TNF-α stimulation in primary endothelial cell culture. To induce hypertension with target-organ damage, we fed mice a high-salt diet and N(omega)-nitro- l -arginine-methyl-ester (L-NAME) and infused angiotensin (Ang) II. This treatment caused a 40-mm Hg blood pressure increase in both Tie-1-ΔN and control mice. In contrast to control mice, Tie-1-ΔN mice developed a milder renal injury, reduced inflammation, and less albuminuria. RT-PCR showed significantly reduced expression of the NF-κB targets VCAM-1 and ICAM-1, compared with control mice. Thus, the data demonstrate a causal link betwe...