Multiple resonance in coupled Duffing oscillators and nonlinear normal modes.

The resonance of N linearly coupled damped Duffing oscillators with a constant frequency sinusoidal driving force acting on the first oscillator is studied analytically by calculating the fixed points of the corresponding dynamical system and numerically using a fourth-order multivariate Runge-Kutta method. For a chain with N oscillators, we establish a general recursion scheme in the form of a system of equations that relates the amplitudes of the oscillators and the driving frequency, capable of describing resonance curves. We consider in detail the case of an oscillator chain with N=2 for high values of the driving amplitude and stiffness, and find hysteretical unstable regions in the resonance curves. In this unstable driving frequency regime, analysis of the time series reveals the presence of nonlinear normal modes visible as beating quasiperiodic oscillations.

Process design and techno-economic analysis of activated carbon derived from anthracite coal.

Activated carbon (AC), renowned for its versatile applications in water treatment, air purification, and industrial processes, is a critical component in environmental remediation and resource recovery strategies. This study encompasses the process modeling of AC production using anthracite coal as a precursor, involving multiple activation stages at different operating conditions, coupled with a detailed techno-economic analysis aimed at assessing the operational feasibility and financial viability of the plant. The economic analysis explores the investigation of economic feasibility by performing a detailed cashflow and sensitivity analysis to identify key parameters influencing the plant's economic performance, including raw material and energy prices, operational and process parameters. Capital and operational costs are meticulously evaluated, encompassing raw material acquisition, labor, energy consumption, and equipment investment. Financial metrics like Net Present Value (NPV), Internal Rate of Return (IRR), and payout period (POP) are employed, and the results show that AC selling price, raw material cost and plant capacity are the most influential parameters determining the plant's feasibility. The minimum AC production cost of 1.28 $/kg is obtained, corresponding to coal flow rate of 14,550 kg/h. These findings provide valuable insights for stakeholders, policymakers, and investors seeking to engage in activated carbon production from anthracite.

Mechanochemical stabilization of heavy metals in fly ash from coal-fired power plants via dry milling and wet milling.

Fly ash from coal-fired power plants has become the world's largest solid waste pollutant. The mechanochemical (MC) method used as a non-thermal method shows good stability to heavy metals in soil and municipal solid waste incineration (MSWI) fly ash. It is first uesd to stabilize the heavy metals in fly ash from coal-fired power plants. In this paper, dry milling and wet milling MC methods were carried out on fly ash from a 300 MW supercritical circulating fluidized bed (CFB) boiler. The relative leaching rate (RLR) is defined to indicate the degree of leaching. Experimental results show that after mechanochemical treatment for 10 h, the RLRs of Cu, Cr, Pb, Zn, Cd, and Ni by dry milling decrease by 52.10%, 70.16%, 89.80%, 22.97%, 3.15%, and 23.49% respectively, and the RLRs of Cu, Cr, Pb, Zn, Cd and Ni by wet milling decrease by 58.11%, 70.92%, 89.64%, 23.26%, 10.59%, and 30.77% respectively. Compared with dry milling, the fly ash particle size is smaller after wet milling, indicating that the presence of water will weaken the agglomeration of fine particles. A continuous extraction experiment shows that the water-and acid-soluble fraction of the six heavy metals in fly ash can be reduced by dry or wet milling, and the residual fraction can be increased.

High performance aqueous supercapacitor based on nitrogen-doped coal-based activated carbon electrode materials.

The performance of a supercapacitor (SCs) fabricated from coal-based activated carbon was studied in terms of its specific capacitance (C), life cycle and rate performance. In this work, a low cost modified nitrogen-doped coal-based activated carbon (MACN) was prepared by KOH/H2O co-activation from lignite. Experimental results and density functional theory (DFT) calculations showed that introducing nitrogen atoms into the coal-based activated carbon leads to a rearrangement of the carbon skeleton structure and changes the surface chemical environment. Leading to the MACN internal disorder increases (ID/IG is up to 0.99), structural stability improves (TGA curves shift right), and various nitrogen functional groups (N-5, N-6, N-Q) are formed on the carbon surface. In addition, the MACN possesses high specific surface area (SBET: 2129 m2/g), abundant micropores (Vmic: 0.62 cm3/g), appropriate mesopores (Vmes: 0.39 cm3/g, Vmes ratio: 38.6%), low impurity content, and highly N-doping (9.59 wt%). These characteristics of the MACN provide for a high C of 323 F/g at a current density of 0.5 A/g. The enhanced MACN is 64.8% higher than the undoped MAC. Furthermore, a high energy density of 10 Wh/kg can be achieved with a MACN-assembled symmetrical cell when the power density of 250 W/kg in 6 M KOH.

An early fault detection method for induced draft fans based on MSET with informative memory matrix selection.

Early fault detection of induced draft (ID) fans is very important to improve the reliability by providing predictive maintenance and reducing unscheduled shutdowns. This study proposed an early fault detection method for ID fans based on MSET with informative memory matrix selection. Firstly, to obtain an informative memory matrix, the discrete particle swarm optimization (DPSO) was utilized to search samples with large condition information. An accurate MSET model was then developed based on the memory matrix to produce predictions of the feature variables. Finally, a similarity index that represents the health status of the equipment was defined to give warnings of early faults. An application to detect the early faults of an ID fan in a coal-fired power plant was demonstrated to illustrate the effectiveness of proposed method.

In-Situ Capture of Mercury in Coal-Fired Power Plants Using High Surface Energy Fly Ash.

Coal-fired power plants represent the largest source of mercury emissions worldwide. Using fly ash, a byproduct of these plants, as a sorbent to remove mercury has proven to be difficult. Here, we found that the fresh surface of modified fly ash has good adsorption performance, and it declines obviously with time because of unsaturation characteristics on surface. On the basis of this mechanism, our study provides a method to in situ capture mercury with high surface energy modified fly ash by mechanochemical and bromide treatment. Fresh modified fly ash with active sites is injected into the flue to directly adsorb mercury. A continuous system within a full-scale 300 MWe plant showed that the mercury adsorption performance of the modified fly ash is similar to that of activated carbon, which is the industry benchmark for the treatment of mercury emission in fossil power generation units. This is a breakthrough and indicates that modified fly ash can become an efficient and convenient industrial sorbent for the removal of mercury.

Disminución del consumo de sal en la población: ¿recomendar o no recomendar?

Resumen La ingesta habitual de sal excede largamente a la necesaria para reponer las pérdidas obligatorias de sodio y cloro por la orina, heces y sudor. A causa de los efectos del sodio sobre la presión arterial se ha señalado al excesivo consumo de sal como uno de los factores que contribuyen a las altas tasas de morbimortalidad cardiovascular que caracterizan a las sociedades actuales, en las que la hipertensión arterial tiene tan elevada prevalencia. En concordancia con esa opinión, distintas prestigiosas instituciones sanitarias y científicas recomiendan a toda la población disminuir el consumo de sal. La Organización Mundial de la Salud recomienda un consumo máximo de 5 g de sal/día, la American Heart Association, un máximo de 3.75 g de sal/día. Las estrategias de disminución de la ingesta de sal, si bien han sido capaces de disminuir la presión arterial, especialmente en los hipertensos, no han logrado en el mundo real resultados consistentes en cuanto a la disminución de la morbimortalidad cardiovascular, y en ciertos casos, los resultados son desfavorables. Esto ha determinado que el tema de recomendar o no en forma universal una disminución del consumo de sal se haya constituido en uno de los puntos más debatidos de la prevención cardiovascular. Análisis recientes de los resultados inconsistentes logrados con la disminución del consumo poblacional de sal permiten vislumbrar una interpretación satisfactoria para esas inconsistencias: las poblaciones con consumos excesivos de sal se beneficiarían con la disminución del consumo, en tanto que las que habitualmente consumen poca sal no se beneficiarían y, hasta en ciertos casos, se podrían perjudicar. En base a estas interpretaciones y aún reconociendo lo difícil que es no ya medir, sino estimar, el consumo individual de sal en la población general, podría recomendarse como medida global un consumo moderado de sal, que quienes consumen sal en exceso disminuyan su consumo y que quienes consumen poca sal, sigan haciéndolo. En los pacientes hipertensos la reducción del consumo de sal disminuye sistemáticamente la incidencia de accidentes cerebrovasculares, pero en relación con otras complicaciones los resultados no son tan consistentes, y debe limitarse la reducción del consumo de sal al suficiente para alcanzar, junto con las otras medidas terapéuticas que correspondan, las metas de presión arterial establecidas para cada situación clínica en particular

Disfunción eréctil y enfermedad cardiovascular / Erectile dysfunction and cardiovascular disease

La disfunción eréctil (DE) pasó de ser considerada un fenómeno de origen psicológico a una manifestación de una enfermedad orgánica. La DE dejó de ser un tema específico de los urólogos para interesar a todos los médicos (y sobre todo a los pacientes) a partir de la popularización de su tratamiento con sildenafil. Los aspectos más conocidos son la interacción del sildenafil (y fármacos similares) con los nitritos y los eventuales riesgos que podría acarrear la actividad sexual en pacientes con cardiopatía. Recientemente se puso de manifiesto la similitud de factores de riesgo de la DE y la enfermedad cardiovascular (CV) y la responsabilidad de la disfunción endotelial, etapa inicial de la enfermedad aterosclerótica en la génesis de la DE. Dado que la DE es, en general, más precoz que la cardiopatía isquémica, es actualmente considerada un factor de riesgo de futuros eventos CV, o, como se la ha catalogado, un "centinela" de la enfermedad CV, con un valor predictivo similar al de los clásicos factores de riesgo CV, y el pene pasó a ser considerado un "barómetro" de la salud endotelial. En esta revisión repasamos la prevalencia de la DE, sus mecanismos de producción, su asociación con otros factores de riesgo y enfermedad CV y su valor como predictor de eventos CV.

El síndrome metabólico / The metabolic syndrome

SÍNDROME X METABOLICO: El síndrome metabólico (SM) es una entidad que empezó a ser vislumbrada hace menos de 30 años y que progresivamente ha ido ganando protagonismo por su elevada prevalencia y su capacidad de predecir riesgos vinculados a la diabetes y las enfermedades cardiovasculares. Ha sido objeto de diversas denominaciones y definiciones, entre las cuales proponemos adoptar la de la International Diabetes Federation. Recientemente se han planteado reservas acerca de su utilidad y se ha puesto en duda la propia naturaleza del SM como entidad. No obstante, aparece con frecuencia creciente en la literatura médica y el concepto de SM se ha popularizado en el conocimiento médico y de la población general, por lo que creemos oportuno revisar las definiciones propuestas, la etiopatogenia, la prevalencia, su capacidad de predicción de riesgos, las recomendaciones para el manejo de los pacientes con SM y las reservas en cuanto a...

Valor pronóstico del test de ejercicio

RESUMEN Introducción: no está bien establecido el valor pronóstico de la ergometría para todas las poblaciones. Objetivos: evaluar la capacidad de la ergometría de predecir eventos cardiovasculares en una población sin limitaciones en sus características. Método: de un total de 1.904 pacientes sometidos a una ergometría en una institución durante el año 1997, se interrogó la evolución a siete años mediante cuestionario estructurado de 524 pacientes (28%), que pudieron ser contactados telefónicamente. Se validó la representatividad del grupo contactado por comparación con los no contactados. Se realizó un análisis bivariado y multivariado de las variables que podrían tener valor predictor de eventos. Con las que resultaron predictores multivariados independientes, se calculó la probabilidad de presentar eventos cardiovasculares utilizando la función logística, y se construyó una tabla de riesgos estimados. Resultados: no encontrando diferencias importantes entre pacientes contactados y no contactados, se aceptó la representatividad del grupo contactado. En cuanto a predicción de eventos, en el análisis bivariado se encontraron diferencias significativas en sexo, edad, antecedentes de hipertensión arterial y dislipidemia, aparición de angor o arritmia en la prueba, o ambas, probabilidad de coronariopatía pre y postest, desnivel ST y frecuencia cardíaca máxima alcanzada. En el multivariado, los predictores independientes fueron: probabilidad pretest, frecuencia cardíaca máxima alcanzada y desnivel ST. Con estas variables se calculó, mediante regresión logística, la probabilidad de presentar eventos cardiovasculares. El área bajo la curva ROC fue 0,801. Se construyó una tabla de riesgos estimados en base a las mismas variables. Conclusiones: se identificaron como predictores independientes de eventos cardiovasculares la probabilidad pretest, frecuencia cardíaca máxima alcanzada y desnivel ST, a partir de los cuales se calculó la probabilidad de sufrir eventos cardiovasculares; estos resultados, en especial la tabla de riesgos estimados, deberían ser validados prospectivamente en una cohorte más numerosa de pacientes.

SUMMARY Background: the prognostic value of stress tests is not well established for every population. Objectives: to establish the capacity of stress tests in the prediction of cardiovascular events in a population without any limitation in its characteristics. Methods: from a total of 1904 patients who underwent a stress test in a institution during 1997, the clinical evolution at 7 seven years of 524 patients (28%) was assessed by using a structured telephonic questionnaire. The representativity of this group was validated by comparison of the characteristics of contacted and no-contacted patients. Bivariate and multivariate analysis of the variables that could have a predictive value was performed. By using the independent multivariate predictive variables the probability of cardiovascular events was calculated through a logistic function and a table of estimated risks was constructed. Results: there were no important differences between contacted and no-contacted patients, so the representativity of the group of contacted patients was accepted. Concerning the prediction of events, there were significant differences in gender, age, history of hypertension and dyslipidemia, angina and/or arrhythmia during the test, pre and posttest probability of coronary heart disease, ST segment deviation and maximal heart rate attained. By multivariate analysis, pretest probability, maximal heart rate and the magnitude of ST segment deviation during the test, were independent predictors of events. Using these variables, through logistic regression, the probability of events was calculated. The area under the ROC curve was 0.801. With the same variables a table of estimated risks was constructed. Conclusions: pretest probability and maximal heart rate and ST deviation during the test were identified as independent predictors of cardiovascular events; with these variables the probability of events was calculated; this results, especially the table of estimated risks, should be prospectively validated in a bigger cohort of patients.