38 research outputs found

    Fast-scale instability of single-stage power-factor-correction power supplies

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    Social Determinants of Community Health Services Utilization among the Users in China: A 4-Year Cross-Sectional Study

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    Background To identify social factors determining the frequency of community health service (CHS) utilization among CHS users in China. Methods Nationwide cross-sectional surveys were conducted in 2008, 2009, 2010, and 2011. A total of 86,116 CHS visitors selected from 35 cities were interviewed. Descriptive analysis and multinomial logistic regression analysis were employed to analyze characteristics of CHS users, frequency of CHS utilization, and the socio-demographic and socio-economic factors influencing frequency of CHS utilization. Results Female and senior CHS clients were more likely to make 3–5 and ≄6 CHS visits (as opposed to 1–2 visits) than male and young clients, respectively. CHS clients with higher education were less frequent users than individuals with primary education or less in 2008 and 2009; in later surveys, CHS clients with higher education were the more frequent users. The association between frequent CHS visits and family income has changed significantly between 2008 and 2011. In 2011, income status did not have a discernible effect on the likelihood of making ≄6 CHS visits, and it only had a slight effect on making 3–5 CHS visits. Conclusion CHS may play an important role in providing primary health care to meet the demands of vulnerable populations in China. Over time, individuals with higher education are increasingly likely to make frequent CHS visits than individuals with primary school education or below. The gap in frequency of CHS utilization among different economic income groups decreased from 2008 to 2011

    Are long working hours associated with weight-related outcomes? A meta-analysis of observational studies

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    The relationship between long working hours and body weight outcomes remains inconclusive; thus, we conducted a meta-analysis to assess the effect of long working hours on weight-related outcomes. PubMed and Embase databases were searched from their inception to June 2019. A random-effects model was used to assess the pooled odds ratio (OR) and corresponding confidence interval (CI). Subgroup analyses and sensitivity analyses were conducted to explore sources of heterogeneity. Publication bias was evaluated by the Begg's and Egger's tests. A total of 29 articles involving 374 863 participants were included. The pooled OR of long working hours on weight-related outcomes was 1.13 (95% CI, 1.07-1.19). In subgroup analysis stratified by definition of outcomes, the pooled ORs of long working hours on “weight gain/BMI increase,” “BMI ≄ 25 kg/m 2,” and “BMI ≄ 30 kg/m 2” were 1.19 (95% CI, 1.02-1.40), 1.07 (95% CI, 1.00-1.14), and 1.23 (95% CI, 1.09-1.39), respectively. We found evidence of publication bias, but correction for this bias using the trim-and-fill method did not alter the combined OR substantially. There was evidence to suggest that long working hours are associated with adverse weight-related outcomes. Preventative interventions such as improved flexibility and healthy working schedules should be established for employees

    The rates and the determinants of hypertension according to the 2017 definition of hypertension by ACC/AHA and 2014 evidence-based guidelines among population aged ≄40 years old

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    Background : In November 2017, the American College of Cardiology/American Heart Association (ACC/AHA) updated their definition of hypertension from 140/90 mm Hg to 130/80 mm Hg. Objectives : We sought to assess the situation of hypertension and the impact of applying the new threshold to a geographically and ethnically diverse population. Methods : We analyzed selected data on 237,142 participants aged ≄40 who had blood pressure taken for the 2014 China National Stroke Screening and Prevention Project. Choropleth maps and logistic regression analyses were performed to estimate the prevalence, geographical distribution and risk factors of hypertension using both 2017 ACC/AHA guidelines and 2014 evidence-based guidelines. Results : The present cross-sectional study showed the age- and sex-standardized prevalence of hypertension was 37.08% and 58.52%, respectively, according to 2014 evidence-based guidelines and 2017 ACC/AHA guidelines. The distribution of hypertension and risk factors changed little between guidelines, with data showing a high prevalence of hypertension around Bohai Gulf and in south central coastal areas using either definition. The age- and sex-standardized prevalence of newly labeled as hypertensive was 21.44%. Interestingly, the high prevalence region of newly labeled as hypertensive was found in the north China. Conclusion : The prevalence of hypertension increased significantly on 2017 ACC/AHA guidelines compared to the prevalence when using 2014 evidence-based guidelines, with high prevalence areas of newly labeled as hypertensive now seen mainly in north China. There need to be correspondingly robust efforts to improve health education, health management, and behavioral and lifestyle interventions in the north

    Evaluation of responsiveness of community health services in urban China: a quantitative study in Wuhan City.

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    BACKGROUND: With the objective of the national health services systems reform to move care to the community, community health services (CHS) are becoming the gateways of the health system in China. This study aims to evaluate the levels and distributions of the responsiveness of CHS in urban China and identify the relevant features to provide the government with policy advice on the improvement of CHS responsiveness. METHODS: A total of 872 face-to-face interviews were conducted in community health centers (CHCs) from 2007 to 2009. Indicators of responsiveness that were recommended by the World Health Organization were adopted, and non-conditional logistic regression analysis was performed to explore the factors associated with the levels and distributions of the responsiveness of CHS. RESULTS: The responsiveness scored at a fairly 'good' level of 7.45, 7.45, and 7.46 for CHS in years 2007, 2008, and 2009, respectively. The representative responsiveness inequality indexes were 0.097, 0.101, and 0.109, respectively, indicating the moderately balanced distributions of responsiveness in these three years. During this period, the scores of responsiveness elements were highest at 7.44 to 8.34 in "dignity", "communication", and "social support", while lowest at 6.76 to 7.54 in "autonomy", "confidentiality", and "basic amenities". The results of the logistic regression analysis suggested that five elements (OR value), namely, "dignity" (1.414-3.345), "communication" (1.218-3.655), "basic amenities" (1.251-2.362), "prompt attention" (1.098-1.590), and "autonomy" (1.416-2.173), had significant associations with CHS responsiveness. CONCLUSIONS: The responsiveness of CHS in Wuhan City was fairly good but still requires further improvement, particularly on the working conditions of CHCs and communication skills trainings among CHS workers

    Adaptive feedback synchronization of a unified chaotic system. Phys Lett A

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    Abstract This Letter further improves and extends the work of Wang et al. [Phys. Lett. A 312 (2003) 34]. In detailed, the linear feedback synchronization and adaptive feedback synchronization with only one controller for a unified chaotic system are discussed here. It is noticed that this unified system contains the noted Lorenz and Chen systems. Two chaotic synchronization theorems are attained. Also, numerical simulations are given to show the effectiveness of these methods

    Fast-scale instability of singlestage power-factor-correction power supplies

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    Abstract—This paper describes the fast-scale bifurcation phenomena of a single-stage power-factor-correction (PFC) power supply which is a cost effective design for low-power applications. The circuit employs a cascade configuration of a boost converter and a forward converter, which share an active switch and operate in discontinuous conduction mode, to provide input PFC and tight output regulation. Main results are illustrated by “exact ” circuit simulations as well as theoretical analysis based on the use of Jacobians. This work provides a convenient means of predicting stability boundaries which can facilitate the selection of practical parameter values for maintaining stable operation. Index Terms—Bifurcation, dc–dc converter, instability, power factor correction (PFC), single-stage converter. I

    Fast-scale bifurcation in single-stage PFC power supplies operating with DCM boost stage and CCM forward stage

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    This paper describes the fast-scale bifurcation phenomena of a single-stage single-switch power-factorcorrection (PFC) regulator comprising a boost stage operating in discontinuous conduction mode (DCM) and a forward stage operating in continuous conduction mode (CCM). The two stages combine into a single stage by sharing one main switch and one control loop. Using ‘exact ’ cycle-by-cycle computer simulations, the e ects of various circuit parameters on fast-scale instabilities are studied. The results are qualitatively veri ed by experimental measurements. This work provides a clear picture of how the variation of certain practical parameters can render such a circuit fast-scale unstable. Copyright? 2006 John Wiley & Sons, Ltd. KEY WORDS: dc–dc converter; power factor correction; single-stage converter; fast-scale instability; bifurcation 1

    Erroneous Results from SPICE Simulations of Switching Converters: A Dynamical System Viewpoint

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    Abstract — The SPICE simulation program is widely used as a brute force simulator for analyzing and designing switching power converters. Results from SPICE are mostly useful, but their integrity is sometimes questionable as erroneous results could be obtained which may not reflect the true behavior of the circuits being simulated. Various parameters in SPICE are crucial in controlling the convergence and accuracy of the simulated results, e.g., relative error tolerance and maximum integration step size. In this paper, we study the system consisting of the SPICE simulation algorithm and the circuit being simulated. Specifically, we describe the generation of flawed solutions in terms of bifurcation of the system under parameter variations. Erroneous results have been collected for different relative error tolerances, maximum integration step sizes, and parasitic inductance and capacitance. These flawed solutions can be analyzed in terms of the manifestation of period-doubling bifurcation and chaotic behavior under variation of selected simulation parameters. This paper provides a systematic approach to rationalizing the behavior of the SPICE simulator, its practical significance being in the identification of the ranges of simulation parameters for which flawed solutions can be produced. I
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