Ignition and Extinction Behavior of Fuels in a Microcombustor
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Shock Tube Test Time Limitation Due to Turbulent-Wall Boundary Layer
Shock tube test time limitation due to the premature arrival of the contact surface is analytically investigated for wholly turbulent-wall boundary layers The results are compared with those for wholly laminar-wall boundary layers It is found that, for a given shock Mach number Ms, the maximum possible test time (in a long shock tube) varies as d 6//4p co1/4 and d2p CD for the turbulent and laminar cases, respectively (d = tube diameter, p oo = initial pressure) For 3 ^ 5, whereas the laminar theory applies, roughly, for dpm ~ 1 (d is in inches; pm is in centimeters of mercury) When dp » 5, turbulent theory for both air and argon indicates test times of about one-half to one-fourth the ideal value for xs/d = 45 to 150, respectively (xs = length of low-pressure section) Higher values of dp » result in more test time When dpm ~ 0 5, laminar theory indicates about one-half ideal test time for xs/d ~ 100 Lower dpm reduces test time Working curves are presented for more accurate estimates of test time in specific cases Boundary-layer closure occurs, in long shock tubes, when Ms < 1 2 and Ms < 3 for laminar and turbulent boundary layers, respectively
Public Hospitals : Options for Reform through Public-Private Partnerships
Globally, health expenditures rose from an average of 3 percent of GDP in 1950 to 8 percent (US$3 trillion) in 1999 (WHO 2000). The increase in spending has been driven by rising income, changing demographic and epidemiological trends, and costly new pharmaceuticals and technology. Although technology is allowing a shift to outpatient care, hospitals still account for 30–50 percent of health expenditures. Public funding has not kept pace with the growth in spending. Much of the increase has been financed from private sources (out-ofpocket payments and private insurance), while the share funded publicly (by tax revenue and national insurance) declined by 6 percent between 1977 and 1997. Constraints on public funding, combined with rising costs, have forced public hospitals to cut costs wherever possible while still endeavoring to guarantee universal (and often free) access to public patients.1 Governments have used different strategies to address these problems, such as shifting financing from general tax revenue to payroll-financed national health insurance, narrowing the basic package of services available to all citizens, linking hospital funding to outputs and efficiency, amalgamating hospitals into networks, increasing autonomy and incentives for management, and reducing the number of hospital beds. Some governments have also turned to public-private partnerships to bring private sector efficiency into public hospitals.