991 resultados para Random variables
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BACKGROUND: quality of life (QoL) is a subjective perception whose components may vary in importance between individuals. Little is known about which domains of QoL older people deem most important. OBJECTIVE: this study investigated in community-dwelling older people the relationships between the importance given to domains defining their QoL and socioeconomic, demographic and health status. METHODS: data were compiled from older people enrolled in the Lc65+ cohort study and two additional, population-based, stratified random samples (n = 5,300). Principal components analysis (PCA) was used to determine the underlying domains among 28 items that participants defined as important to their QoL. The components extracted were used as dependent variables in multiple linear regression models to explore their associations with socioeconomic, demographic and health status. RESULTS: PCA identified seven domains that older persons considered important to their QoL. In order of importance (highest to lowest): feeling of safety, health and mobility, autonomy, close entourage, material resources, esteem and recognition, and social and cultural life. A total of six and five domains of importance were significantly associated with education and depressive symptoms, respectively. The importance of material resources was significantly associated with a good financial situation (β = 0.16, P = 0.011), as was close entourage with living with others (β = 0.20, P = 0.007) and as was health and mobility with age (β = -0.16, P = 0.014). CONCLUSION: the importance older people give to domains of their QoL appears strongly related to their actual resources and experienced losses. These findings may help clinicians, researchers and policy makers better adapt strategies to individuals' needs.
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PURPOSE: To meta-analyze the literature on the clinical performance of Class V restorations to assess the factors that influence retention, marginal integrity, and marginal discoloration of cervical lesions restored with composite resins, glass-ionomer-cement-based materials [glass-ionomer cement (GIC) and resin-modified glass ionomers (RMGICs)], and polyacid-modified resin composites (PMRC). MATERIALS AND METHODS: The English literature was searched (MEDLINE and SCOPUS) for prospective clinical trials on cervical restorations with an observation period of at least 18 months. The studies had to report about retention, marginal discoloration, marginal integrity, and marginal caries and include a description of the operative technique (beveling of enamel, roughening of dentin, type of isolation). Eighty-one studies involving 185 experiments for 47 adhesives matched the inclusion criteria. The statistical analysis was carried out by using the following linear mixed model: log (-log (Y /100)) = β + α log(T ) + error with β = log(λ), where β is a summary measure of the non-linear deterioration occurring in each experiment, including a random study effect. RESULTS: On average, 12.3% of the cervical restorations were lost, 27.9% exhibited marginal discoloration, and 34.6% exhibited deterioration of marginal integrity after 5 years. The calculation of the clinical index was 17.4% of failures after 5 years and 32.3% after 8 years. A higher variability was found for retention loss and marginal discoloration. Hardly any secondary caries lesions were detected, even in the experiments with a follow-up time longer than 8 years. Restorations placed using rubber-dam in teeth whose dentin was roughened showed a statistically significantly higher retention rate than those placed in teeth with unprepared dentin or without rubber-dam (p < 0.05). However, enamel beveling had no influence on any of the examined variables. Significant differences were found between pairs of adhesive systems and also between pairs of classes of adhesive systems. One-step self-etching had a significantly worse clinically index than two-step self-etching and three-step etch-and-rinse (p = 0.026 and p = 0.002, respectively). CONCLUSION: The clinical performance is significantly influenced by the type of adhesive system and/or the adhesive class to which the system belongs. Whether the dentin/enamel is roughened or not and whether rubberdam isolation is used or not also significantly influenced the clinical performance. Composite resin restorations placed with two-step self-etching and three-step etch-and-rinse adhesive systems should be preferred over onestep self-etching adhesive systems, GIC-based materials, and PMRCs.
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Study of the changes in health habits of 105 cancer patients’ relatives and close friends after the diagnosis. The aim is to try to verify whether the knowledge of the disease has got some impact in the modification of their life styles. The emotional alterations influence in this change of behaviour has been analysed futhermore. An interview of own creation and HADS (Anxiety Hospital and Depression Scale of Zigmond and Snaith, 1983) instrument, in a Spanish and a Catalan version, were used with this aim. The results show that 21.1% of the participants presented positive changes in their health habits after the diagnosis of the relative or close friend and 11.5% showed negative changes. In relation to the role of the emotions, averages of anxiety (14,33; d.t.=4,98) and depressive (10,17; d.t.=4,93) symptoms were higher in those subjects who made negative changes than in those who did not make any change (9,32; d.t.=5,37 and 6,33; d.t.=4,64). In addition, the youngest participants, with more depressive symptoms and who visit the subject more often, are those who become more assets modifying health habits. The results suggest that emotional alterations, mainly depressive symptoms, are associated with negative change and, therefore, it would be suitable to lend some type of attention to these alterations in the population studied with the purpose of improving their present and future health
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The CO2-laser-MAG hybrid welding process has been shown to be a productive choice for the welding industry, being used in e.g. the shipbuilding, pipe and beam manufacturing, and automotive industries. It provides an opportunity to increase the productivity of welding of joints containing air gaps compared with autogenous laser beam welding, with associated reductions in distortion and marked increases in welding speeds and penetration in comparison with both arc and autogenous laser welding. The literature study indicated that the phenomena of laser hybrid welding are mostly being studied using bead-on-plate welding or zero air gap configurations. This study shows it very clearly that the CO2 laser-MAG hybrid welding process is completely different, when there is a groove with an air gap. As in case of industrial use it is excepted that welding is performed for non-zero grooves, this study is of great importance for industrial applications. The results of this study indicate that by using a 6 kW CO2 laser-MAG hybrid welding process, the welding speed may also be increased if an air gap is present in the joint. Experimental trials indicated that the welding speed may be increased by 30-82% when compared with bead-on-plate welding, or welding of a joint with no air gap i.e. a joint prepared as optimum for autogenous laser welding. This study demonstrates very clearly, that the separation of the different processes, as well as the relative configurations of the processes (arc leading or trailing) affect welding performance significantly. These matters influence the droplet size and therefore the metal transfer mode, which in turn determined the resulting weld quality and the ability to bridge air gaps. Welding in bead-onplate mode, or of an I butt joint containing no air gap joint is facilitated by using a leading torch. This is due to the preheating effect of the arc, which increases the absorptivity of the work piece to the laser beam, enabling greater penetration and the use of higher welding speeds. With an air gap present, air gap bridging is more effectively achieved by using a trailing torch because of the lower arc power needed, the wider arc, and the movement of droplets predominantly towards the joint edges. The experiments showed, that the mode of metal transfer has a marked effect on gap bridgeability. Transfer of a single droplet per arc pulse may not be desirable if an air gap is present, because most of the droplets are directed towards the middle of the joint where no base material is present. In such cases, undercut is observed. Pulsed globular and rotational metal transfer modes enable molten metal to also be transferred to the joint edges, and are therefore superior metal transfer modes when bridging air gaps. It was also found very obvious, that process separation is an important factor in gap bridgeability. If process separation is too large, the resulting weld often exhibits sagging, or no weld may be formed at all as a result of the reduced interaction between the component processes. In contrast, if the processes are too close to one another, the processing region contains excess molten metal that may create difficulties for the keyhole to remain open. When the distance is optimised - i.e. a separation of 0-4 mm in this study, depending on the welding speed and beam-arc configuration - the processes act together, creating beneficial synergistic effects. The optimum process separation when using a trailing torch was found to be shorter (0-2 mm) than when a leading torch is used (2-4 mm); a result of the facilitation of weld pool motion when the latter configuration is adopted. This study demonstrates, that the MAG process used has a strong effect on the CO2-laser-MAG hybrid welding process. The laser beam welding component is relatively stable and easy to manage, with only two principal processing parameters (power and welding speed) needing to be adjusted. In contrast, the MAG process has a large number of processing parameters to optimise, all of which play an important role in the interaction between the laser beam and the arc. The parameters used for traditional MAG welding are often not optimal in achieving the most appropriate mode of metal transfer, and weld quality in laser hybrid welding, and must be optimised if the full range of benefits provided by hybrid welding are to be realised.
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In this study, a wrapper approach was applied to objectively select the most important variables related to two different anaerobic digestion imbalances, acidogenic states and foaming. This feature selection method, implemented in artificial neural networks (ANN), was performed using input and output data from a fully instrumented pilot plant (1 m 3 upflow fixed bed digester). Results for acidogenic states showed that pH, volatile fatty acids, and inflow rate were the most relevant variables. Results for foaming showed that inflow rate and total organic carbon were among the relevant variables, both of which were related to the feed loading of the digester. Because there is not a complete agreement on the causes of foaming, these results highlight the role of digester feeding patterns in the development of foaming
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Sobriety checkpoints are not usually randomly located by traffic authorities. As such, information provided by non-random alcohol tests cannot be used to infer the characteristics of the general driving population. In this paper a case study is presented in which the prevalence of alcohol-impaired driving is estimated for the general population of drivers. A stratified probabilistic sample was designed to represent vehicles circulating in non-urban areas of Catalonia (Spain), a region characterized by its complex transportation network and dense traffic around the metropolis of Barcelona. Random breath alcohol concentration tests were performed during spring 2012 on 7,596 drivers. The estimated prevalence of alcohol-impaired drivers was 1.29 PER CENT, which is roughly a third of the rate obtained in non-random tests. Higher rates were found on weekends (1.90 PER CENT on Saturdays, 4.29 PER CENT on Sundays) and especially at night. The rate is higher for men (1.45 PER CENT) than for women (0.64 PER CENT) and the percentage of positive outcomes shows an increasing pattern with age. In vehicles with two occupants, the proportion of alcohol-impaired drivers is estimated at 2.62 PER CENT, but when the driver was alone the rate drops to 0.84 PER CENT, which might reflect the socialization of drinking habits. The results are compared with outcomes in previous surveys, showing a decreasing trend in the prevalence of alcohol-impaired drivers over time.
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All social surveys suffer from different types of errors, of which one of the most studied is non-response bias. Non-response bias is a systematic error that occurs because individuals differ in their accessibility and propensity to participate in a survey according to their own characteristics as well as those from the survey itself. The extent of the problem heavily depends on the correlation between response mechanisms and key survey variables. However, non-response bias is difficult to measure or to correct for due to the lack of relevant data about the whole target population or sample. In this paper, non-response follow-up surveys are considered as a possible source of information about non-respondents. Non-response follow-ups, however, suffer from two methodological issues: they themselves operate through a response mechanism that can cause potential non-response bias, and they pose a problem of comparability of measure, mostly because the survey design differs between main survey and non-response follow-up. In order to detect possible bias, the survey variables included in non-response surveys have to be related to the mechanism of participation, but not be sensitive to measurement effects due to the different designs. Based on accumulated experience of four similar non-response follow-ups, we studied the survey variables that fulfill these conditions. We differentiated socio-demographic variables that are measurement-invariant but have a lower correlation with non-response and variables that measure attitudes, such as trust, social participation, or integration in the public sphere, which are more sensitive to measurement effects but potentially more appropriate to account for the non-response mechanism. Our results show that education level, work status, and living alone, as well as political interest, satisfaction with democracy, and trust in institutions are pertinent variables to include in non-response follow-ups of general social surveys. - See more at: https://ojs.ub.uni-konstanz.de/srm/article/view/6138#sthash.u87EeaNG.dpuf
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Problems related to fire hazard and fire management have become in recent decades one of the most relevant issues in the Wildland-Urban Interface (WUI), that is the area where human infrastructures meet or intermingle with natural vegetation. In this paper we develop a robust geospatial method for defining and mapping the WUI in the Alpine environment, where most interactions between infrastructures and wildland vegetation concern the fire ignition through human activities, whereas no significant threats exist for infrastructures due to contact with burning vegetation. We used the three Alpine Swiss cantons of Ticino, Valais and Grisons as the study area. The features representing anthropogenic infrastructures (urban or infrastructural components of the WUI) as well as forest cover related features (wildland component of the WUI) were selected from the Swiss Topographic Landscape Model (TLM3D). Georeferenced forest fire occurrences derived from the WSL Swissfire database were used to define suitable WUI interface distances. The Random Forest algorithm was applied to estimate the importance of predictor variables to fire ignition occurrence. This revealed that buildings and drivable roads are the most relevant anthropogenic components with respect to fire ignition. We consequently defined the combination of drivable roads and easily accessible (i.e. 100 m from the next drivable road) buildings as the WUI-relevant infrastructural component. For the definition of the interface (buffer) distance between WUI infrastructural and wildland components, we computed the empirical cumulative distribution functions (ECDF) of the percentage of ignition points (observed and simulated) arising at increasing distances from the selected infrastructures. The ECDF facilitates the calculation of both the distance at which a given percentage of ignition points occurred and, in turn, the amount of forest area covered at a given distance. Finally, we developed a GIS ModelBuilder routine to map the WUI for the selected buffer distance. The approach was found to be reproducible, robust (based on statistical analyses for evaluating parameters) and flexible (buffer distances depending on the targeted final area covered) so that fire managers may use it to detect WUI according to their specific priorities.
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Muscular function of the neck region may be of importance for the etiology of headache, especially of tension-type headache. However, very few data exist on the association of neck muscle function with different types of headache in adolescents. The main aim of the study was to examine the association of neck muscle function with adolescent headache. The associations between leisure time activities, endurance strength of the upper extremities (UE endurance) and mobility of the neck-shoulder region and adolescent headache were studied. In addition, the associations of force production, EMG/force ratio, co-activation and fatigue characteristics, and cross-sectional area (CSA) of neck muscles with adolescent headache were studied. The study is part of a population-based cohort study of 12-year-old children with and without headache. The study had five phases (years 1998-2003). At the age of 13 years, a sample of 183 adolescents (183/311) participated in endurance strength and mobility measurements of the neck-shoulder region. In addition, the type and level of physical and other leisure activity were elicited with open and structured questions. At the age of 17 years, a random sample of 89 adolescents (89/202) participated in force and EMG measurements of the neck-shoulder muscles. In addition, at the age of 17 years, a sample of 65 adolescents (65/89) participated in CSA measurements of the neck muscles. At the age of 13 years, intensive participation in overall sports activity was associated with migraine. Frequent computer use was associated both with migraine and tension-type headache. The type of sports or other leisure activity classified them on the basis of body loading was not associated with headache type. In girls, low UE endurance of both sides, and low cervical rotation of the dominant side, were associated with tension-type headache, and low UE endurance of non-dominant side with migraine. In boys, no associations occurred between UE endurance and mobility variables and headache types. At the age of 17 years, in girls, high EMG/force ratios between the EMG of the left agonist sternocleidomastoid muscle (SCM) and maximal neck flexion and neck rotation force to the right side as well as high co-activation of right antagonist cervical erector spinae (CES) muscles during maximal neck flexion force were associated with migraine-type headache. In girls, neck force production was not associated with headache types but low left shoulder flexion force was associated with tension-type headache. In boys, no associations were found between EMG and force variables and headache. Increased SCM muscles fatigue of both sides was associated with tension-type headache. In boys, the small CSA of the right SCM muscle and, in girls, of combined right SCM and scalenus muscles was associated with tension-type headache. Similarly, in boys, the large CSA of the right SCM muscle, of the combined right SCM and scalenus muscles, of the left semispinalis capitis muscle, of the combined left semispinalis and splenius muscles was associated with migraine. No other differences in the CSA of neck flexion or extension muscles were found. Differences in the neuromucular function of the neck-shoulder muscles were associated with adolescent headache, especially in girls. Differences in the cross-sectional area of unilateral neck muscles were associated with headache, especially in boys. Differences in the neuromuscular function and in the cross-sectional area of the neck muscles also occurred between different types of headache. It remains to be established whether the findings are primary or secondary to adolescent migraine and tension headache. Keywords: adolescent, cross-sectional area, electromyography, endurance strength, fatigue, force, headache, leisure time activity, migraine, mobility, neck muscles, tension-type headache
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1. Digital elevation models (DEMs) are often used in landscape ecology to retrieve elevation or first derivative terrain attributes such as slope or aspect in the context of species distribution modelling. However, DEM-derived variables are scale-dependent and, given the increasing availability of very high-resolution (VHR) DEMs, their ecological relevancemust be assessed for different spatial resolutions. 2. In a study area located in the Swiss Western Alps, we computed VHR DEMs-derived variables related to morphometry, hydrology and solar radiation. Based on an original spatial resolution of 0.5 m, we generated DEM-derived variables at 1, 2 and 4 mspatial resolutions, applying a Gaussian Pyramid. Their associations with local climatic factors, measured by sensors (direct and ambient air temperature, air humidity and soil moisture) as well as ecological indicators derived fromspecies composition, were assessed with multivariate generalized linearmodels (GLM) andmixed models (GLMM). 3. Specific VHR DEM-derived variables showed significant associations with climatic factors. In addition to slope, aspect and curvature, the underused wetness and ruggedness indices modelledmeasured ambient humidity and soilmoisture, respectively. Remarkably, spatial resolution of VHR DEM-derived variables had a significant influence on models' strength, with coefficients of determination decreasing with coarser resolutions or showing a local optimumwith a 2 mresolution, depending on the variable considered. 4. These results support the relevance of using multi-scale DEM variables to provide surrogates for important climatic variables such as humidity, moisture and temperature, offering suitable alternatives to direct measurements for evolutionary ecology studies at a local scale.
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Une Suisse polycentrique et multifonctionnelle ou du fédéralisme coopératif à la concurrence fiscale.
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PURPOSE: We investigated association of hematological variables with specific fitness performance in elite team-sport players. METHODS: Hemoglobin mass (Hbmass) was measured in 25 elite field hockey players using the optimized (2 min) CO-rebreathing method. Hemoglobin concentration ([Hb]), hematocrit and mean corpuscular hemoglobin concentration (MCHC) were analyzed in venous blood. Fitness performance evaluation included a repeated-sprint ability (RSA) test (8 x 20 m sprints, 20 s of rest) and the Yo-Yo intermittent recovery level 2 (YYIR2). RESULTS: Hbmass was largely correlated (r = 0.62, P<0.01) with YYIR2 total distance covered (YYIR2TD) but not with any RSA-derived parameters (r ranging from -0.06 to -0.32; all P>0.05). [Hb] and MCHC displayed moderate correlations with both YYIR2TD (r = 0.44 and 0.41; both P<0.01) and RSA sprint decrement score (r = -0.41 and -0.44; both P<0.05). YYIR2TD correlated with RSA best and total sprint times (r = -0.46, P<0.05 and -0.60, P<0.01; respectively), but not with RSA sprint decrement score (r = -0.19, P>0.05). CONCLUSION: Hbmass is positively correlated with specific aerobic fitness, but not with RSA, in elite team-sport players. Additionally, the negative relationships between YYIR2 and RSA tests performance imply that different hematological mechanisms may be at play. Overall, these results indicate that these two fitness tests should not be used interchangeably as they reflect different hematological mechanisms.
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We present a model for transport in multiply scattering media based on a three-dimensional generalization of the persistent random walk. The model assumes that photons move along directions that are parallel to the axes. Although this hypothesis is not realistic, it allows us to solve exactly the problem of multiple scattering propagation in a thin slab. Among other quantities, the transmission probability and the mean transmission time can be calculated exactly. Besides being completely solvable, the model could be used as a benchmark for approximation schemes to multiple light scattering.
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En este documento se formula un modelo de predicción de la insolvencia a través de la combinación de diferentes variables cuantitativas extraídas de los estados contables de una muestra de empresas para los años 1994-1997. Partiendo del modelo de flexibilidad financiera de Donaldson, que es adaptado por Van Frederikslust a la predicción de la insolvencia, lo que aquí se expone es una aplicación a una muestra de empresas de los sectores textil y confección. Aunque los resultados no son alentadores, lo más importante es destacar cómo a través de una modelización de este tipo, probamos una formulación teórica del problema.