Global burden and strength of evidence for 88 risk factors in 204 countries and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Understanding the health consequences associated with exposure to risk factors is necessary to inform public health policy and practice. To systematically quantify the contributions of risk factor exposures to specific health outcomes, the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 aims to provide comprehensive estimates of exposure levels, relative health risks, and attributable burden of disease for 88 risk factors in 204 countries and territories and 811 subnational locations, from 1990 to 2021. Methods: The GBD 2021 risk factor analysis used data from 54 561 total distinct sources to produce epidemiological estimates for 88 risk factors and their associated health outcomes for a total of 631 risk–outcome pairs. Pairs were included on the basis of data-driven determination of a risk–outcome association. Age-sex-location-year-specific estimates were generated at global, regional, and national levels. Our approach followed the comparative risk assessment framework predicated on a causal web of hierarchically organised, potentially combinative, modifiable risks. Relative risks (RRs) of a given outcome occurring as a function of risk factor exposure were estimated separately for each risk–outcome pair, and summary exposure values (SEVs), representing risk-weighted exposure prevalence, and theoretical minimum risk exposure levels (TMRELs) were estimated for each risk factor. These estimates were used to calculate the population attributable fraction (PAF; ie, the proportional change in health risk that would occur if exposure to a risk factor were reduced to the TMREL). The product of PAFs and disease burden associated with a given outcome, measured in disability-adjusted life-years (DALYs), yielded measures of attributable burden (ie, the proportion of total disease burden attributable to a particular risk factor or combination of risk factors). Adjustments for mediation were applied to account for relationships involving risk factors that act indirectly on outcomes via intermediate risks. Attributable burden estimates were stratified by Socio-demographic Index (SDI) quintile and presented as counts, age-standardised rates, and rankings. To complement estimates of RR and attributable burden, newly developed burden of proof risk function (BPRF) methods were applied to yield supplementary, conservative interpretations of risk–outcome associations based on the consistency of underlying evidence, accounting for unexplained heterogeneity between input data from different studies. Estimates reported represent the mean value across 500 draws from the estimate's distribution, with 95% uncertainty intervals (UIs) calculated as the 2·5th and 97·5th percentile values across the draws. Findings: Among the specific risk factors analysed for this study, particulate matter air pollution was the leading contributor to the global disease burden in 2021, contributing 8·0% (95% UI 6·7–9·4) of total DALYs, followed by high systolic blood pressure (SBP; 7·8% [6·4–9·2]), smoking (5·7% [4·7–6·8]), low birthweight and short gestation (5·6% [4·8–6·3]), and high fasting plasma glucose (FPG; 5·4% [4·8–6·0]). For younger demographics (ie, those aged 0–4 years and 5–14 years), risks such as low birthweight and short gestation and unsafe water, sanitation, and handwashing (WaSH) were among the leading risk factors, while for older age groups, metabolic risks such as high SBP, high body-mass index (BMI), high FPG, and high LDL cholesterol had a greater impact. From 2000 to 2021, there was an observable shift in global health challenges, marked by a decline in the number of all-age DALYs broadly attributable to behavioural risks (decrease of 20·7% [13·9–27·7]) and environmental and occupational risks (decrease of 22·0% [15·5–28·8]), coupled with a 49·4% (42·3–56·9) increase in DALYs attributable to metabolic risks, all reflecting ageing populations and changing lifestyles on a global scale. Age-standardised global DALY rates attributable to high BMI and high FPG rose considerably (15·7% [9·9–21·7] for high BMI and 7·9% [3·3–12·9] for high FPG) over this period, with exposure to these risks increasing annually at rates of 1·8% (1·6–1·9) for high BMI and 1·3% (1·1–1·5) for high FPG. By contrast, the global risk-attributable burden and exposure to many other risk factors declined, notably for risks such as child growth failure and unsafe water source, with age-standardised attributable DALYs decreasing by 71·5% (64·4–78·8) for child growth failure and 66·3% (60·2–72·0) for unsafe water source. We separated risk factors into three groups according to trajectory over time: those with a decreasing attributable burden, due largely to declining risk exposure (eg, diet high in trans-fat and household air pollution) but also to proportionally smaller child and youth populations (eg, child and maternal malnutrition); those for which the burden increased moderately in spite of declining risk exposure, due largely to population ageing (eg, smoking); and those for which the burden increased considerably due to both increasing risk exposure and population ageing (eg, ambient particulate matter air pollution, high BMI, high FPG, and high SBP). Interpretation: Substantial progress has been made in reducing the global disease burden attributable to a range of risk factors, particularly those related to maternal and child health, WaSH, and household air pollution. Maintaining efforts to minimise the impact of these risk factors, especially in low SDI locations, is necessary to sustain progress. Successes in moderating the smoking-related burden by reducing risk exposure highlight the need to advance policies that reduce exposure to other leading risk factors such as ambient particulate matter air pollution and high SBP. Troubling increases in high FPG, high BMI, and other risk factors related to obesity and metabolic syndrome indicate an urgent need to identify and implement interventions. Funding: Bill & Melinda Gates Foundation

Geometrical Design Considerations on Externally Pressurized Porous Gas Bearings

This study investigates the influences of geometrical effects on the performance of a finite length porous journal bearing fed by externally pressurized air. The analysis in this study considers three geometrical parameters, L/D, H/D, and C/R, as the main influence factors. A quasi-linear numerical scheme associated with an underrelaxation factor is used to solve for the pressure solutions of the nonlinear coupled partial differential equation (PDE). Results show that the porous journal bearing exhibits a significant aerodynamic lubrication action when L/D epsilon 1, H/D epsilon 0.1, and 0.0005 C/R 0.001. This study recommends L/D = 1 and C/R = 0.001 as optimum design criteria for the bearing aspect ratio and clearance ratio, respectively, as far as bearing load and whirling instability are concerned. Because greater porous thickness does not improve the bearing load capacity, this study suggests H/D = 0.1 as a proper porous thickness

Experimental study on heat transfer and friction in pin fin channel flow

Experimental work is conducted to examine the effect of porosity, originated from the theory of the porous medium flow, on both the heat transfer rate and friction behavior for flow through a pin fin channel. Four units of the pin fin matrix having different porosities are used in the flow test. The heat transfer rates are obtained using the LMTD method. It is found that the hear transfer rate is higher for flow through a high porosity pin fin matrix, which possesses a higher heating surface area. For a relatively large Reynolds number flow, the friction factors are found to depend only on the flow porosity due to the presence of the roughness-like pin fin protruding through the viscous sublayer. Average friction factors are then suggested for every pin fin channel

Characteristics of Externally Pressurized Porous Gas Bearings Considering Structure Permeability

The performance of a finite length porous journal bearing fed by externally pressurized air is numerically analyzed in the present study. A quasi-linear numerical scheme associated with an underrelaxation factor is used to solve the pressure solutions of the nonlinear coupled partial differential equation (PDE). Two characteristic parameters, i.e., the feeding parameter p and a conventional bearing number , are involved in the analysis. The results show that the aerodynamic lubricating effect is dominant for the porous bearing having a small p number, whereas the aerostatic effect prevails inside the bearing space as the p number is large. When the permeability parameter p is small, the aerodynamic effect is further promoted for the bearing operating at heavy load; herein the minimum film thickness becomes relatively small. It is found that a bearing with a small p will have a higher risk for the journal shaft to touch the bearing wall than a bearing with large p. Therefore, as far as the bearing safety and loading capacity are concerned, a porous journal bearing with p ranging between 0.5 and 1 is recommended in practical use

Determination of solid material elastic modulus and surface energy based on JKR contact model

The JKR contact theory is employed to study the adhesion phenomena between two solid materials in intimate contact. The elastic contact modulus and the work of adhesion of solid materials are obtained during adhesion tests by utilizing a micro force-deflection measuring apparatus. Six of the plastic materials, including polyethylene polyoxymethlene (POM), polyamide (PA), terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), and ultra-high molecular weight polyethylene (UHMWPE) are used to evaluate the adhesion effect implied by the JKR theory. Comparison is made between surface energy obtained from the adhesion tests with that by a dynamic contact angle analyser. Results show that the load/deflection data in the loading phase are in good agreement with the predictions of JKR equation, and the experimental data of unloading phase deviate significantly from the JKR theory. The phenomena of adhesion hysteresis in loading tests are responsible for these results due to the effects of molecular reconstruction on solid surfaces in contact. The work of adhesions, and hence surface energies of plastic materials, calculated by the best fitting of JKR equation with the experimental data in the loading phase, agree satisfactorily in a comparable manner with that obtained using the contact angle analyser. (c) 2007 Elsevier B.V. All rights reserved

Adhesion strength and wear resistance of a Al2O3 films deposited on 440C stainless steel

The adhesion strength and wear resistance of coated films are examined in this work. Protective films made of Al2O3 ceramic oxide are deposited by sol-gel spin coating on the substrates of 440C stainless steel. The effects of substrate surface roughness and film hardening temperature on the coating characteristics are investigated. The adhesion strength of the film-substrate system is assessed by measuring. the adhesion using a contact angle analyzer. Comparisons are made between the adhesion results and the critical loads obtained by scratch test. The wear resistance to sliding contact is represented by the wear weight loss of the coated film determined in a pin-on-disk test. The experimental results show that the ceramic films coated on smoother metallic surface strengthen the adhesive bonding between the substrate and the deposited film. The films coated on the smooth substrate and hardened at some high sintering temperature are experimentally determined to have high wear resistance to sliding contact