CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments.

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation-calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the looping-calcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant, whereas for nonpretreated sorbents the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data for CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation-calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation of the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum conversion in a small number of cycles, is explained in light of the model.

Role of particle size on the multicycle calcium looping activity of limestone for thermochemical energy storage.

The calcium looping process, based on the reversible reaction between CaCO3 and CaO, is recently attracting a great deal of interest as a promising thermochemical energy storage system to be integrated in Concentrated Solar Power plants (CaL-CSP). The main drawbacks of the system are the incomplete conversion of CaO and its sintering-induced deactivation. In this work, the influence of particle size in these deactivation mechanisms has been assessed by performing experimental multicycle tests using standard limestone particles of well-defined and narrow particle size distributions. The results indicate that CaO multicycle conversion benefits from the use of small particles mainly when the calcination is carried out in helium at low temperature. Yet, the enhancement is only significant for particles below 15 µm. On the other hand, the strong sintering induced by calcining in CO2 at high temperatures makes particle size much less relevant for the multicycle performance. Finally, SEM imaging reveals that the mechanism responsible for the loss of activity is mainly pore-plugging when calcination is performed in helium, whereas extensive loss of surface area due to sintering is responsible for the deactivation when calcination is carried out in CO2 at high temperature.

Pull-off force of coated fine powders under small consolidation.

In this paper, a three-dimensional model taking into account the contact deformation and surface area coverage (SAC) of nanoadditives is proposed to predict the force required to separate two contacting particles (the pull-off force) under consolidation stress up to 10 KPa, for cornstarch, a Geldart group C powder, sparsely and densely dry-coated with nanosilica. The experimental pull-off force measurement is conducted in a Seville powder tester. Comparison of the predicted results with the experimental results indicates (1) that the pull-off force of sparsely coated cornstarch is larger than that of densely coated cornstarch due to the greater hardness and small particle radius of fumed silica; (2) there is not a continuous variation in the pull-off force with the coverage of silica; on the contrary, values of the pull-off force of sparsely coated samples are grouped in similar range, while the values of the pull-off force of densely coated samples are grouped in another range of lower values. (3) Within a range, the SAC does not have a big effect on the pull-off force for sparsely coated samples and only a slight effect for densely coated samples (4) the pull-off force increases with increasing consolidation force due to larger deformation in the contact area; (5) under consolidation stresses up to 10 KPa, the deformation of the cornstarch particles is not large enough to fully embed the nanosized silica.

IL-6 and IGF-1 are independent prognostic factors of liver steatosis and non-alcoholic steatohepatitis in morbidly obese patients.

BACKGROUND: Lipid accumulation and other histological liver markers characterize patients with non-alcoholic steatohepatitis (NASH). The identification of non-invasive prognostic factors of liver steatosis and NASH are relevant for the unravelling of the mechanisms of this disease, as well as for the clinical diagnoses of these patients. METHODS: 36 patients with morbid obesity and 12 healthy subjects were consecutively enrolled in this cross-sectional study to determine the serological parameters associated with the degree of hepatic steatosis and NASH. Clinical, biochemical and histologic variables were examined in blood and liver biopsies by descriptive, univariate and multivariate regression analysis. RESULTS: The patients were distributed as non-NASH (14), probably-NASH (13) and NASH (9), according to the Non-alcoholic fatty liver disease Activity Score (NAS). The study identified remarkable differences in liver steatosis, and glucose, insulin, IL-6 and IGF-1 concentrations in blood among patients with morbid obesity. IL-6 was correlated with the degree of liver steatosis until the morbidly obese patients fulfil the criteria of NASH. The patients with NASH reduced IL-6 concentration in blood. IGF-1 decreased throughout the progression of NASH. TNF-alpha concentration was not related to liver steatosis or NASH in morbidly obese patients. The multivariate regression analysis identified glucose >110 mg/dL, IL-6 >4.81 pg/mL and IGF-1 <130 ng/mL, and homeostasis model assessment (HOMA) >4.5 and IGF-1 <110 ng/mL as independent predictors of hepatic steatosis and NASH, respectively. CONCLUSIONS: The concentration of glucose, insulin, IL-6 and IGF-1 in blood are useful markers for the selection of patients with liver steatosis or NASH.

Development and validation of a multivariate predictive model for rheumatoid arthritis mortality using a machine learning approach.

We developed and independently validated a rheumatoid arthritis (RA) mortality prediction model using the machine learning method Random Survival Forests (RSF). Two independent cohorts from Madrid (Spain) were used: the Hospital Clínico San Carlos RA Cohort (HCSC-RAC; training; 1,461 patients), and the Hospital Universitario de La Princesa Early Arthritis Register Longitudinal study (PEARL; validation; 280 patients). Demographic and clinical-related variables collected during the first two years after disease diagnosis were used. 148 and 21 patients from HCSC-RAC and PEARL died during a median follow-up time of 4.3 and 5.0 years, respectively. Age at diagnosis, median erythrocyte sedimentation rate, and number of hospital admissions showed the higher predictive capacity. Prediction errors in the training and validation cohorts were 0.187 and 0.233, respectively. A survival tree identified five mortality risk groups using the predicted ensemble mortality. After 1 and 7 years of follow-up, time-dependent specificity and sensitivity in the validation cohort were 0.79-0.80 and 0.43-0.48, respectively, using the cut-off value dividing the two lower risk categories. Calibration curves showed overestimation of the mortality risk in the validation cohort. In conclusion, we were able to develop a clinical prediction model for RA mortality using RSF, providing evidence for further work on external validation.

Pulse wave velocity in four extremities for assessing cardiovascular risk using a new device.

Pulse wave velocity (PWV) is used for evaluating atherosclerosis; however, it is far from routine use. The authors validate a new device measuring PWV independently in each limb and explore its usefulness. Validity was studied in 40 patients. PWV was compared with endovascular measurements and comparisons were made between PWV in the extremities in 220 patients. The correlation between brachial PWV and endovascular catheter was (r=0.83, P<.001). The correlation coefficients for interobserver and intraobserver were r=0.87 and r=0.91, respectively. The sum of PWV in limbs allowed better stratification of patients according to cardiovascular risk. The validity and reproducibility of PWV measured with this device was good. The sum of PWV in extremities was a good index for stratifying patients according to vascular risk. These results suggest that the device is useful in the evaluation of arteriosclerosis and could possibly replace measurement devices available today.

Prevalencia y factores asociados con el episodio depresivo en adolescentes de la población urbana de tres ciudades de la Sierra Peruana 2003 / Prevalence and associated factors with a depressive episode in adolescents from the population of three cities of the Peruvian Andes

La depresión en adolescentes constituye un problema de salud pública por su frecuencia creciente y sus consecuencias. Objetivo: Determinar las prevalencias y los factores asociados con el episodio depresivo en adolescentes de las ciudades de Cajamarca, Huaraz y Ayacucho. Material y Métodos: Estudio epidemiológico de corte transversal, con muestreo probabilístico trietápico por conglomerados. Se usó la base de datos del Estudio Epidemiológico en Salud Mental de la Sierra Peruana 2003. La población estudiada comprendió a los residentes de 12 a 17 años. Se utilizaron cuestionarios para medir variables demográficas y socioeconómicas, aspectos generales de salud mental, trastornos clínicos y relaciones intrafamiliares. Se ajustaron modelos de regresión logística múltiple. Resultados: La prevalencia de episodio depresivo en adolescentes fue 5,7% (IC 95%: 4,5%-7,2%), observándose según el análisis multivariado, asociaciones estadísticamente significativas con: sexo femenino (OR: 2,7, IC 95%: 1,4-5,2), haber tenido enamorado(a) (OR: 2,3, IC 95%: 1,2-4,1), síndrome psicótico (OR: 5,3, IC 95%: 2,2-13,2) y deseos de morir (OR: 3,2, IC 95%: 1,8-5,8). Conclusiones: La prevalencia de episodio depresivo en adolescentes de las tres ciudades estudiadas fue similar a la encontrada en otros países. Los factores asociados que mejor predijeron el episodio depresivo fueron: sexo femenino, haber tenido enamorado(a), síndrome psicótico y deseos de morir alguna vez en la vida; los cuales podrían ser evaluados como factores de riesgo en estudios posteriores.

Adolescent depression is a public health problem due to its increasing frequency and consequences. Objective: To determine the prevalence of depressive episode and associated factors in adolescents from the cities of Cajamarca, Huaraz and Ayacucho. Material and Methods: Cross sectional study with three-stage cluster probability sampling. We used the database of the Mental Health Epidemiological Study from the Peruvian Andes 2003. The population from 12 to 17 years old was assessed. Questionnaires were used to measure demographic and socioeconomic variables, general mental health, mental disorders and domestic relationships. We adjusted multiple logistic regression models. Results: Prevalence of depressive episode in adolescents was 5.7% (IC 95%: 4.5%-7.2%). We observed by multivariate analysis, statistically significant associations with: female gender (OR: 2.7, IC 95%: 1.4-5.2), having had a boyfriend or girlfriend (OR: 2.3, IC 95%: 1.2-4.1), psychotic syndrome (OR: 5.3, IC 95%: 2.2-13.2) and the wish to die (OR: 3.2, IC 95%: 1.8-5.8). Conclusions: Prevalence of depressive episode in adolescents in these three cities was similar to those reported in adolescents in other countries. Associated factors that best predicted depressive episode were female gender, having had a boyfriend or girlfriend, psychotic syndrome and wish to die, which should be evaluated as risk factors in future studies.