Recent observations suggest that a large fraction of the energy density of the universe has negative pressure. One explanation is vacuum energy density; another is quintessence in the form of a scalar field slowly evolving down a potential. In either case, a key problem is to explain why the energy density nearly coincides with the matter density today. The densities decrease at different rates as the universe expands, so coincidence today appears to require that their ratio be set to a specific, infinitessimal value in the early universe. In this paper, we introduce the notion of a "tracker field," a form of quintessence, and show how it may explain the coincidence, adding new motivation for the quintessence scenario.A number of recent observations suggest that Ω m , the ratio of the (baryonic plus dark) matter density to the critical density, is significantly less than unity.1 Either the universe is open, or there is some additional energy density ρ sufficient to reach Ω total = 1, as predicted by inflation. Measurements of the cosmic microwave background, the mass power spectrum, 1-3 and, most explicitly, the luminosity-red shift relation observed for Type Ia supernovae, 4 all suggest that the missing energy should possess negative pressure (p) and equationof-state (w ≡ p/ρ). One candidate for the missing energy is vacuum energy density or cosmological constant, Λ for which w = −1. The resulting cosmological model, ΛCDM, consists of a mixture of vacuum energy and cold dark matter. Another possibility is QCDM cosmologies based on a mixture of cold dark matter and quintessence (−1 < w ≤ 0), a slowly-varying, spatially inhomogeneous component.7 An example of quintessence is the energy associated with a scalar field (Q) slowly evolving down its potential V (Q).5-8 Slow evolution is needed to obtain negative pressure, p = 1 2Q 2 − V (Q), so that the kinetic energy density is less than the potential energy density.Two difficulties arise from all of these scenarios. The first is the fine-tuning problem: Why is the missing energy density today so small compared to typical particle physics scales? If Ω m ∼ 0.3 today the missing energy density is of order 10 −47 GeV 4 , which appears to require the introduction of new mass scale 14 or so orders of magnitude smaller than the electroweak scale. A second difficulty is the "cosmic coincidence" problem:9 Since the missing energy density and the matter density decrease at different rates as the universe expands, it appears that their ratio must be set to a specific, infinitessimal value in the very early universe in order for the two densities to nearly coincide today, some 15 billion years later.What seems most ideal is a model in which the energy density in the Q-component is comparable to the radiation density (to within a few order of magnitude) at the end of inflation, say. If there were some rough equipartition of energy following reheating among several thousands of degrees of freedom, one might expect the energy density of the Q-component to be two or so orders of ma...

IMPORTANCE Noncommunicable chronic diseases have become the leading causes of mortality and disease burden worldwide. OBJECTIVE To investigate the prevalence of diabetes and glycemic control in the Chinese adult population. DESIGN, SETTING, AND PARTICIPANTS Using a complex, multistage, probability sampling design, we conducted a cross-sectional survey in a nationally representative sample of 98 658 Chinese adults in 2010. MAIN OUTCOMES AND MEASURES Plasma glucose and hemoglobin A 1c levels were measured after at least a 10-hour overnight fast among all study participants, and a 2-hour oral glucose tolerance test was conducted among participants without a self-reported history of diagnosed diabetes. Diabetes and prediabetes were defined according to the 2010 American Diabetes Association criteria; whereas, a hemoglobin A 1c level of <7.0% was considered adequate glycemic control. RESULTS The overall prevalence of diabetes was estimated to be 11.6% (95% CI, 11.3%-11.8%) in the Chinese adult population. The prevalence among men was 12.1% (95% CI, 11.7%-12.5%) and among women was 11.0% (95% CI, 10.7%-11.4%). The prevalence of previously diagnosed diabetes was estimated to be 3.5% (95% CI, 3.4%-3.6%) in the Chinese population: 3.6% (95% CI, 3.4%-3.8%) in men and 3.4% (95% CI, 3.2%-3.5%) in women. The prevalence of undiagnosed diabetes was 8.1% (95% CI, 7.9%-8.3%) in the Chinese population: 8.5% (95% CI, 8.2%-8.8%) in men and 7.7% (95% CI, 7.4%-8.0%) in women. In addition, the prevalence of prediabetes was estimated to be 50.1% (95% CI, 49.7%-50.6%) in Chinese adults: 52.1% (95% CI, 51.5%-52.7%) in men and 48.1% (95% CI, 47.6%-48.7%) in women. The prevalence of diabetes was higher in older age groups, in urban residents, and in persons living in economically developed regions. Among patients with diabetes, only 25.8% (95% CI, 24.9%-26.8%) received treatment for diabetes, and only 39.7% (95% CI, 37.6%-41.8%) of those treated had adequate glycemic control. CONCLUSIONS AND RELEVANCE The estimated prevalence of diabetes among a representative sample of Chinese adults was 11.6% and the prevalence of prediabetes was 50.1%. Projections based on sample weighting suggest this may represent up to 113.9 million Chinese adults with diabetes and 493.4 million with prediabetes. These findings indicate the importance of diabetes as a public health problem in China.

Background Public health is a priority for the Chinese Government. Evidence-based decision making for health at the province level in China, which is home to a fifth of the global population, is of paramount importance. This analysis uses data from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 to help inform decision making and monitor progress on health at the province level. Methods We used the methods in GBD 2017 to analyse health patterns in the 34 province-level administrative units in China from 1990 to 2017. We estimated all-cause and cause-specific mortality, years of life lost (YLLs), years lived with disability (YLDs), disability-adjusted life-years (DALYs), summary exposure values (SEVs), and attributable risk. We compared the observed results with expected values estimated based on the Socio-demographic Index (SDI). Findings Stroke and ischaemic heart disease were the leading causes of death and DALYs at the national level in China in 2017. Age-standardised DALYs per 100 000 population decreased by 33•1% (95% uncertainty interval [UI] 29•8 to 37•4) for stroke and increased by 4•6% (-3•3 to 10•7) for ischaemic heart disease from 1990 to 2017. Agestandardised stroke, ischaemic heart disease, lung cancer, chronic obstructive pulmonary disease, and liver cancer were the five leading causes of YLLs in 2017. Musculoskeletal disorders, mental health disorders, and sense organ diseases were the three leading causes of YLDs in 2017, and high systolic blood pressure, smoking, high-sodium diet, and ambient particulate matter pollution were among the leading four risk factors contributing to deaths and DALYs. All provinces had higher than expected DALYs per 100 000 population for liver cancer, with the observed to expected ratio ranging from 2•04 to 6•88. The all-cause age-standardised DALYs per 100 000 population were lower than expected in all provinces in 2017, and among the top 20 level 3 causes were lower than expected for ischaemic heart disease, Alzheimer's disease, headache disorder, and low back pain. The largest percentage change at the national level in age-standardised SEVs among the top ten leading risk factors was in high body-mass index (185%, 95% UI 113•1 to 247•7]), followed by ambient particulate matter pollution (88•5%, 66•4 to 116•4). Interpretation China has made substantial progress in reducing the burden of many diseases and disabilities. Strategies targeting chronic diseases, particularly in the elderly, should be prioritised in the expanding Chinese health-care system.

IMPORTANCEPrevious studies have shown increasing prevalence of diabetes in China, which now has the world's largest diabetes epidemic.OBJECTIVES To estimate the recent prevalence and to investigate the ethnic variation of diabetes and prediabetes in the Chinese adult population. DESIGN, SETTING, AND PARTICIPANTS A nationally representative cross-sectional survey in 2013 in mainland China, which consisted of 170 287 participants.EXPOSURES Fasting plasma glucose and hemoglobin A 1c levels were measured for all participants. A 2-hour oral glucose tolerance test was conducted for all participants without diagnosed diabetes. MAIN OUTCOMES AND MEASURESPrimary outcomes were total diabetes and prediabetes defined according to the 2010 American Diabetes Association criteria. Awareness and treatment were also evaluated. Hemoglobin A 1c concentration of less than 7.0% among treated diabetes patients was considered adequate glycemic control. Minority ethnic groups in China with at least 1000 participants (Tibetan, Zhuang, Manchu, Uyghur, and Muslim) were compared with Han participants.RESULTS Among the Chinese adult population, the estimated standardized prevalence of total diagnosed and undiagnosed diabetes was 10.9% (95% CI, 10.4%-11.5%); that of diagnosed diabetes, 4.0% (95% CI, 3.6%-4.3%); and that of prediabetes, 35.7% (95% CI, 34.1%-37.4%). Among persons with diabetes, 36.5% (95% CI, 34.3%-38.6%) were aware of their diagnosis and 32.2% (95% CI, 30.1%-34.2%) were treated; 49.2% (95% CI, 46.9%-51.5%) of patients treated had adequate glycemic control. Tibetan and Muslim Chinese had significantly lower crude prevalence of diabetes than Han participants (14.7% [95% CI, 14.6%-14.9%] for Han, 4.3% [95% CI, 3.5%-5.0%] for Tibetan, and 10.6% [95% CI, 9.3%-11.9%] for Muslim; P < .001 for Tibetan and Muslim compared with Han). In the multivariable logistic models, the adjusted odds ratios compared with Han participants were 0.42 (95% CI, 0.35-0.50) for diabetes and 0.77 (95% CI, 0.71-0.84) for prediabetes for Tibetan Chinese and 0.73 (95% CI, 0.63-0.85) for diabetes and 0.78 (95% CI, 0.71-0.86) for prediabetes in Muslim Chinese.CONCLUSIONS AND RELEVANCE Among adults in China, the estimated overall prevalence of diabetes was 10.9%, and that for prediabetes was 35.7%. Differences from previous estimates for 2010 may be due to an alternate method of measuring hemoglobin A 1c .

A substantial fraction of the energy density of the universe may consist of quintessence in the form of a slowly-rolling scalar field. Since the energy density of the scalar field generally decreases more slowly than the matter energy density, it appears that the ratio of the two densities must be set to a special, infinitesimal value in the early universe in order to have the two densities nearly coincide today. Recently, we introduced the notion of tracker fields to avoid this initial conditions problem. In the paper, we address the following questions: What is the general condition to have tracker fields? What is the relation between the matter energy density and the equation-of-state of the universe imposed by tracker solutions? And, can tracker solutions explain why quintessence is becoming important today rather than during the early universe?