Comparative study of four sigmoid models of pressure-volume curve in acute lung injury

BACKGROUND: The pressure-volume curve of the respiratory system is a tool to monitor and set mechanical ventilation in acute lung injury. Mathematical models of the static pressure-volume curve of the respiratory system have been proposed to overcome the inter- and intra-observer variability derived from eye-fitting. However, different models have not been compared. METHODS: The goodness-of-fit and the values of derived parameters (upper asymptote, maximum compliance and points of maximum curvature) in four sigmoid models were compared, using pressure-volume data from 30 mechanically ventilated patients during the early phase of acute lung injury. RESULTS: All models showed an excellent goodness-of-fit (R(2 )always above 0.92). There were significant differences between the models in the parameters derived from the inspiratory limb, but not in those derived from the expiratory limb of the curve. The within-case standard deviations of the pressures at the points of maximum curvature ranged from 2.33 to 6.08 cmH(2)O. CONCLUSION: There are substantial variabilities in relevant parameters obtained from the four different models of the static pressure-volume curve of the respiratory system

Prediction of Lateral Displacements Induced by Liquefaction in the Port of Manzanillo, Mexico During the Earthquake of October 9, 1995

This paper presents the prediction of the lateral displacements due to liquefaction in the yards of the Container Terminal at San Pedrito in the Mexican port of Manzanillo during the earthquake of October 9, 1995 (Ms=7.3, Mw=8.0). It describes briefly the results of field and laboratory tests carried out after the earthquake in order to obtain the required parameters to compute lateral displacements using the Newmark model and a modified Newmark block analysis which takes account of dilatant behavior; the models were calibrated with results of centrifuge experiments. Field data and simplified liquefaction analysis showed that the liquefied fill had a thickness of 13 m and a gentle slope of one degree. From the laboratory tests a yielding shear stress of 3.3 kPa was estimated, and from seismic risk analyses the input used for the prediction of the lateral displacements was a sinusoidal wave of twenty two cycles of constants amplitude of 3.25 m/s2 at a frequency of 1.4 Hz. Since in the case of Manzanillo the laboratory results did not show evidence of dilatant behavior, the original Newmark sliding block analysis was used and predicted a lateral displacements of 1.95 m, which is in good agreement with the actual movements (slightly higher than 2 m) observed after the earthquake

Optimization of Nanoparticle-Based SERS Substrates through Large-Scale Realistic Simulations

Surface-enhanced Raman scattering (SERS) has become a widely used spectroscopic technique for chemical identification, providing unbeaten sensitivity down to the singlemolecule level. The amplification of the optical near field produced by collective electron excitations plasmons in nanostructured metal surfaces gives rise to a dramatic increase by many orders of magnitude in the Raman scattering intensities from neighboring molecules. This effect strongly depends on the detailed geometry and composition of the plasmonsupporting metallic structures. However, the search for optimized SERS substrates has largely relied on empirical data, due in part to the complexity of the structures, whose simulation becomes prohibitively demanding. In this work, we use state-of-the-art electromagnetic computation techniques to produce predictive simulations for a wide range of nanoparticle-based SERS substrates, including realistic configurations consisting of random arrangements of hundreds of nanoparticles with various morphologies. This allows us to derive rules of thumb for the influence of particle anisotropy and substrate coverage on the obtained SERS enhancement and optimum spectral ranges of operation. Our results provide a solid background to understand and design optimized SERS substrates.Peer ReviewedPostprint (published version

Germinación y crecimiento inicial de Fabáceas arbustivas de Galicia en relación con los usos tradicionales, los cambios ambientales y la edad de las semillas

Esta memoria de tesis doctoral se pretende analizar la respuesta germinativa y el crecimiento inicial de siete Fabáceas arbustivas características de comunidades de matorral de Galicia, a factores relacionados con los usos tradicionales y la edad de las semillas. Para ello se ha evaluado el efecto que produce sobre las semillas el tratamiento de Insolación, Arena y gradientes experimentales de estrés hídrico en relación con los suelos de Galicia; y que estos pueden repercutir en el mantenimiento de las comunidades de las que forman parte. Las leguminosas arbustivas son muy adecuadas para las rotaciones agrosilvopastoral así como para la restauración mejorando la fertilización del suelo pretendiendo conocer su variación de germinación en semillas recién recogidas en unas condiciones de fotoperiodo y de oscuridad. Por último, el estudio llevado a cabo del crecimiento inicial consiste en caracterizar morfológicamente las especies analizando los tres primeros meses de desarrollo de las plántulas que han sido previamente sembradas tras llevar a cabo una escarificación y disponer en bandejas forestales que han sido tratados con diferentes niveles de sequías en los dos últimos meses de crecimiento en unas condiciones ambientales controladas. Se evaluó la producción de semillas, la germinación, emergencia, desarollo inicial de las hojas, biomasa aérea y subterránea, relaciones estructurales y tasas de crecimiento durante tres meses

Formation of PoIycyclic Soils During the Recent Quaternary on Monte Borrelho (Northern Portugal)

[Abstract] Pedological and palynological characterization oftwo soils from Monte Borrelho (northern Portugal) evidences the formation ofpolycyclic soils in the Subatlantic. In both soils, two cycles are clearly separated by a stone line which may have resulted either from climatic deterioration or because human activity led to severe deforestation and the consequent preferential development ofherbaceous and shrub vegetation. Either cause would have favoured intense erosion, removing part of the upper A horizon of the pre-existing soils and giving rise to profiles with polycyclic characteristics

Modelling the contact propagation of nosocomial infection in emergency departments

The nosocomial infection is a special kind of infection that is caused by microorganisms acquired inside a hospital. In the daily care process of an emergency department, the interactions between patients and sanitary staff create the environment for the transmission of such microorganisms. Rates of morbility and mortality due to nosocomial infections areimportant indicators of the quality of hospital work. In this research, we use Agent Based Modeling and Simulation techniques to build a model of Methicillinresistant Staphylococcus Aureus propagation based on an Emergency Department Simulator which has been tested and validated previously. The model obtained will allow us to build a contact propagation simulator that enables the construction of virtual environments with theaim of analyzing how the prevention policies affect the rate of propagation of nosocomial infectionPeer Reviewe

An Agent-Based Decision Support System for Hospitals Emergency Departments

AbstractModeling and simulation have been shown to be useful tools in many areas of the Healthcare operational management, field in which there is probably no area more dynamic and complex than hospital emergency departments (ED). This paper presents the results of an ongoing project that is being carried out by the Research Group in Individual Oriented Modeling (IoM) of the University Autonoma of Barcelona (UAB) with the participation of Hospital of Sabadell ED Staff Team. Its general objective is creating a simulator that, used as decision support system (DSS), aids the heads of the ED to make the best informed decisions possible. The defined ED model is a pure Agent-Based Model, formed entirely of the rules governing the behavior of the individual agents which populate the system. Two distinct types of agents have been identified, active and passive. Active agents represent human actors, meanwhile passive agents represent services and other reactive systems. The actions of agents and the communication between them will be represented using Moore state machines extended to include probabilistic transitions. The model also includes the environment in which agents move and interact. With the aim of verifying the proposed model an initial simulation has been created using NetLogo, an agent-based simulation environment well suited for modeling complex systems

Simulation Optimization for Healthcare Emergency Departments

AbstractThis article presents an Agent-Based modeling (ABM) simulation to design a decision support system (DSS) for Healthcare Emergency Department (ED). This DSS aims to aid EDs heads in setting up management guidelines to improve the operation of EDs. This ongoing research is being performed by the Research Group in Individual Oriented Modeling (IoM) at the University Autonoma of Barcelona (UAB) with close collaboration of Hospital ED Staff Team. The objective of the proposed ABM procedure is to optimize the performance of such complex and dynamic Healthcare EDs, because worldwide most of them are overcrowded, and unable to provide ad hoc care, quality and service. Exhaustive search (ES) optimization is used to find out the optimal ED staff configuration, which includes doctors, triage nurses, and admission personnel, i.e., a multidimensional problem. An index is proposed to minimize patient length of stay in the ED. The results obtained by using an alternative pipeline scheme to ES are promising and a better understanding of the problem is achieved. The impact of the pipeline scheme to reduce the computational cost of exhaustive search is outlined

Using an Agent-based Simulation for Predicting the Effects of Patients Derivation Policies in Emergency Departments

AbstractThe increasing demand of urgent care, overcrowding of hospital emergency departments (ED) and limited economic resources are phenomena shared by health systems around the world. It is estimated that up to 50% of patients that are attended in ED have non complex conditions that could be resolved in ambulatory care services. The derivation of less complex cases from the ED to other health care devices seems an essential measure to allocate properly the demand of care service between the different care units. This paper presents the results of an experiment carried out with the objective of analyzing the effects on the ED (patients’ Length of Stay, the number of patients attended and the level of activity of ED Staff) of different derivation policies. The experiment has been done with data of the Hospital of Sabadell (a big hospital, one of the most important in Catalonia, Spain), making use of an Agent-Based model and simulation formed entirely of the rules governing the behaviour of the individual agents which populate the ED, and due to the great amount of data that should be computed, using High Performance Computing