537 research outputs found
On tiered small jump operators
Predicative analysis of recursion schema is a method to characterize
complexity classes like the class FPTIME of polynomial time computable
functions. This analysis comes from the works of Bellantoni and Cook, and
Leivant by data tiering. Here, we refine predicative analysis by using a
ramified Ackermann's construction of a non-primitive recursive function. We
obtain a hierarchy of functions which characterizes exactly functions, which
are computed in O(n^k) time over register machine model of computation. For
this, we introduce a strict ramification principle. Then, we show how to
diagonalize in order to obtain an exponential function and to jump outside
deterministic polynomial time. Lastly, we suggest a dependent typed
lambda-calculus to represent this construction
Estudio del efecto del fluido sobre las frecuencias naturales y modos de vibración de agitador 4PBT45 mediante simulación numérica
En el presente trabajo, se estudian los efectos de diferentes fenómenos físicos sobre las
frecuencias naturales de un agitador 4PBT45 (modificado en estudios preliminares para
obtener un bajo consumo de potencia y alto grado de mezcla) utilizando la herramienta de
simulación computacional ANSYS Mechanical, a partir de escenarios simplificados en
diferentes condiciones de operación. El proyecto comienza con el análisis de los álabes
aislados, para luego estudiar el comportamiento del impulsor por separado y verificar qué
sucede con los modos de vibración. Se realiza la simplificación del impulsor a un rotor
axisimétrico, con la misma masa y momento de inercia polar, para comparar los efectos
en contraste con el agitador original, a través de escenarios estáticos y dinámicos en
vacío de cada uno de los modelos. Además, se realiza el modelamiento numérico del
agitador estático sumergido y se prueban diferentes propiedades de fluidos.
Prácticamente, las variables que se monitorean son: cómo gobiernan las frecuencias
locales de los álabes sobre el impulsor, en base al factor de participación de masa; cuáles
modos de vibración se ven afectados por la rotación en vacío y cuánto varían las
frecuencias debido a dicho fenómeno y por qué; cuán factible es reemplazar el impulsor
por un disco y en qué casos da buenos resultados; y cuánto repercute el efecto del fluido
envolvente sobre las frecuencias naturales en el sistema estático y cómo se comportan
para diferentes tipos de fluidos. En general, se determina que las frecuencias naturales
varían en diferentes cantidades dependiendo del fenómeno estudiado. Algunas
frecuencias tienden a disminuir o a aumentar en diferentes grados conforme se
incrementan las revoluciones, mientras que otras se mantienen constantes. También, se
determina que casi todas las frecuencias disminuyen entre 0.5% y 20% por el efecto del
fluido dependiendo principalmente de la densidad del mismo y del modo de vibrar. Por
otro lado, se encuentra una expresión analítica que permite calcular la frecuencia natural
bajo el efecto de un fluido B, conociendo la frecuencia dentro de un fluido A, a partir de la
relación de sus densidades, bajo ciertas hipótesis y condiciones. Además, se consigue
una variación entre 1% y 6% entre las frecuencias obtenidas mediante simulación
numérica y las calculadas analíticamente, reduciendo el sistema a un grado de libertad,
para los modos más importantes. Por último, se conocen los alcances de la herramienta
computacional en este tipo de simulaciones y sus limitaciones para desarrollar escenarios
más complejos.Tesi
Eccentricity fluctuations and elliptic flow at RHIC
Fluctuations in nucleon positions can affect the spatial eccentricity of the
overlap zone in nucleus-nucleus collisions. We show that elliptic flow should
be scaled by different eccentricities depending on which method is used for the
flow analysis. These eccentricities are estimated semi-analytically. When
is analyzed from 4-particle cumulants, or using the event plane from directed
flow in a zero-degree calorimeter, the result is shown to be insensitive to
eccentricity fluctuations.Comment: 5 pages, 3 eps figure
Laser Noise Reduction in Air
Fluctuations of the white-light supercontinuum produced by ultrashort laser
pulses in selfguided filaments (spatio-temporal solitons) in air are
investigated. We demonstrate that correlations exist within the white-light
supercontinuum, and that they can be used to significantly reduce the laser
intensity noise by filtering the spectrum. More precisely, the fundamental
wavelength is anticorrelated with the wings of the continuum, while conjugated
wavelength pairs on both sides of the continuum are strongly correlated.
Spectral filtering of the continuum reduces the laser intensity noise by 1.2
dB, showing that fluctuations are rejected to the edges of the spectrum.Comment: 8 page
Use of Transition Probabilities to Estimate the Effect of Smoking on the Duration of Episodes of Respiratory Symptoms in Diary Data: The Swiss Study on Air Pollution and Lung Diseases in Adults (SAPALDIA)
Incompletely documented symptom episodes pose methodological problems in the analysis of diary data. The aim of this study was to develop a method of estimating the average durations of symptomatic and nonsymptomatic episodes, respectively, coping with the problem of bias due to undocumented days and censored episodes that is found in most diary studies. The authors derived their outcome variables from a Markov model using transition probabilities. To evaluate this method, the authors assessed the impact of active smoking on the duration of episodes of bronchitis symptoms and the corresponding nonsymptomatic periods, respectively, using diary data (1992-1993) obtained from 801 participants in the Swiss Study on Air Pollution and Lung Diseases in Adults. Covariate-adjusted distribution curves for the mean durations of individual episodes were estimated by Cox regression. Median values for light smokers (<10 cigarettes/day) were 60.0 sympton-free days (95% confidence interval (CI) 42.0-78.5) and 4.0 symptomatic days (95% CI 3.0-6.0), respectively, compared with medians of only 21.0 days 95% CI 16.2-29.8) for periods without bronchitis symptoms and 6.0 days (95% CI 4.9-9.0) for episodes of bronchitis symptoms in heavy smokers(≥30 cigarettes/day). The authors suggest that the Markov method is a feasible approach to the assessment of long term effects of smoking and environmental risk factors on the average duration of symptomatic and nonsymptomatic respiratory episodes. Am J Epidemiol 1998;148:600-
Effects of passive smoking on heart rate variability, heart rate and blood pressure: an observational study
Background Exposure to environmental tobacco smoke (ETS) has been shown to increase the risk for cardiovascular diseases and death, and autonomic dysfunction (specifically, reduced heart rate variability (HRV)) is a predictor of increased cardiac risk. This study tests the hypothesis that ETS exposure reduces HRV in the general population and discusses possible pathways. Methods This cross-sectional study was conducted between 2001 and 2003 and is part of the SAPALDIA (Swiss Cohort Study on Air Pollution and Lung Diseases in Adults) study. The analysis included 1218 randomly selected non-smokers aged 50 and above who participated in 24-h electrocardiogram recordings. Other examinations included an interview, investigating health status (especially respiratory and cardiovascular health and health relevant behaviours and exposure to ETS) and measurements of blood pressure, body height and weight. Results Subjects exposed to ETS at home or at work for more than 2 h/day had a difference of −15% in total power (95%CI: −26 to −3%), low frequency power (−28 to −1%), low/high frequency ratio (−26 to −3%) and −18% (−29 to −4%) in ultralow frequency power of HRV compared with subjects not exposed to ETS at home or work. We also found a 2.7% (−0.01 to 5.34%) higher heart rate during the recording in exposed subjects. Conclusions Exposure to ETS at home and work is associated with lower HRV and with higher heart rate in an ageing population. Our findings suggest that exposure to ETS increases cardiac risk through disturbances in the autonomic nervous syste
Effect of physical activity on heart rate variability in normal weight, overweight and obese subjects: results from the SAPALDIA study
Many studies have demonstrated an association of both a sedentary lifestyle and a high body mass index (BMI) with greater risk for cardiovascular disease. Within the prospective SAPALDIA cohort (Swiss cohort Study on Air Pollution and Lung Diseases in Adults), we investigated whether regular exercise was protective against reduced heart rate variability (HRV), a clinically relevant predictor of cardiovascular morbidity and mortality, and whether adverse effects of obesity and weight gain on HRV were modified by regular exercise. Twenty-four-hour electrocardiograms were recorded in 1,712 randomly selected SAPALDIA participants aged ≥50, for whom BMI was assessed in the years 1991 and 2001-2003. Other examinations included an interview investigating health status (especially respiratory and cardiovascular health and health relevant behaviours including physical activity) and measurements of blood pressure, body height and weight. The association between regular physical activity and HRV and interactions with BMI and BMI change was assessed in multivariable linear regression analyses. Compared to sedentary obese subjects, SDNN (standard deviation of all RR intervals) was 14% (95% CI: 8-20%) higher in sedentary normal weight subjects; 19% (CI: 12-27%) higher in normal weight subjects exercising regularly ≥2h/week; and 19% (CI: 11-28%) higher in obese subjects exercising regularly ≥2h/week. Compared with sedentary subjects who gained weight, those who gained weight but did exercise regularly had a 13% higher SDNN (CI: 7-20%). Regular physical exercise has strong beneficial effects on cardiac autonomic nervous function and thus appears to offset the negative effect of obesity on HR
Eccentricity and elliptic flow in proton-proton collisions from parton evolution
It has been argued that high-multiplicity proton-proton collisions at the LHC
may exhibit collective phenomena usually studied in the context of heavy-ion
collisions, such as elliptic flow. We study this issue using DIPSY - a Monte
Carlo event generator based on the QCD dipole model. We calculate the
eccentricity of the transverse area defined by the spatial distribution of
produced gluons. The resulting elliptic flow is estimated to be about 6%,
comparable to the value in nucleus-nucleus collisions at RHIC and the LHC.
Experimentally, elliptic flow is inferred from the azimuthal correlation
between hadrons, which receives contributions from collective flow, and from
various other effects referred to as "nonflow". We discuss how to identify in
experiments the signal of flow in the presence of large nonflow effects.Comment: v2: Four-particle correlation added, improved discussions on the
signatures of flow. v3: Improved treatment of fluctuations in the flow
analysis. v4: Minor changes for journal submissio
The Urine-to-Plasma Urea Concentration Ratio is associated with eGFR and eGFR decline over time in a population cohort.
BACKGROUND
Evaluation of renal function and of factors associated with its decline are important public health issues. Besides markers of glomerular function (e.g., GFR), those of tubular functions are rarely evaluated. Urea, the most abundant urinary solute, is markedly concentrated in urine when compared to plasma. We explored the urine-to-plasma ratio of urea concentrateions (U/P-urea-ratio) as a marker of tubular functions.
METHODS
We evaluated the relationship of the U/P-urea-ratio with eGFR at baseline in 1043 participants (48±17y) from the SKIPOGH population-based cohort, using mixed regression. In 898 participants, we assessed the relation between U/P-urea-ratio and renal function decline between two study waves 3 years apart. We studied U/P ratios for osmolarity, Na, K, uric acid for comparison.
RESULTS
In a transversal study at baseline, eGFR was positively associated with U/P-urea-ratio (βscaled = 0.08, 95%CI[0.04;0.13]) but not with the U/P ratio of osmolarity. Considering separately participants with renal function > or ≤ 90 ml/minx1.73m2, this association was observed only in those with reduced renal function. In the longitudinal study, eGFR declined at a mean rate of 1.2 ml/min per year. A significant association was observed between baseline U/P-urea-ratio and eGFR decline (βscaled = 0.08, 95%CI[0.01;0.15]). A lower baseline U/P-urea-ratio was associated with a greater eGFR decline.
CONCLUSION
This study provides evidence that the U/P-urea-ratio is an early marker of kidney function decline in the general adult population. Urea is easy to measure with well-standardized techniques and at low cost. Thus, the U/P-urea-ratio could become an easily available tubular marker for evaluating renal function decline
Prevalence of renal impairment and its association with cardiovascular risk factors in a general population: results of the Swiss SAPALDIA study
Background. Impaired renal function is evolving as an independent marker of the risk of cardiovascular morbidity and mortality. Little is known about the prevalence of impaired renal function and its relationship to cardiovascular risk factors in the Swiss general population. Methods. SAPALDIA comprises a random sample of the Swiss population established in 1991, originally to investigate the health effects of long-term exposure to air pollution. Participants were reassessed in 2002/3 and blood measurements were obtained (n = 6317). Renal function was estimated using the Cockcroft-Gault equation and the modified MDRD (four-component) equation incorporating age, race, gender and serum creatinine level. Results. The estimated prevalence of impaired renal function [estimated glomerular filtration rate <60 ml/min/1.73 m2] differed substantially between men and women, particularly at higher ages, and amounted to 13% [95% confidence interval (CI) 10-16%] and 36% (95% CI 32-40%) in men and women, respectively, of 65 years or older. Smoking, obesity, blood lipid levels, high systolic blood pressure and hyperuricaemia were all more common in men when compared with women. These cardiovascular risk factors were also associated independently with creatinine in both women and men. Women were less likely to receive cardiovascular drugs, in particular angiotensin-converting enzyme inhibitors and β-blockers, when compared with men of the same age. Conclusion. Moderate renal impairment seems to be prevalent in the general population, with an apparent excess in females which is not explained by conventional cardiovascular risk factors. The unexpected finding questions the validity of the prediction equations, in particular in female
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