Last data update: May 13, 2024. (Total: 46773 publications since 2009)
Records 1-7 (of 7 Records) |
Query Trace: Zipf G[original query] |
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Collection and laboratory methods for dried blood spots for hemoglobin A1c and total and high-density lipoprotein cholesterol in population based surveys
Miller IM , Lacher DA , Chen TC , Zipf GW , Gindi RM , Galinsky AM , Nwankwo T , Terry AL . Clin Chim Acta 2015 445 143-54 BACKGROUND: The Health Measures at Home Study was a study designed to evaluate the feasibility of incorporating dried blood spots (DBS) collection into the National Health Interview Survey and to compare the proficiencies between field interviewers and health technicians in obtaining DBS. METHODS: DBS collection and venipuncture were attempted on 125 participants. The DBS were collected in the participant's home and venous blood was collected in the National Health and Nutrition Examination Survey (NHANES) mobile examination center. The DBS results were compared to venous results in the NHANES for the measurements of hemoglobin A1c (HbA1c) and total and high-density lipoprotein (HDL) cholesterol. RESULTS: Field interviewers and health technicians were able to collect the DBS for greater than 95% of participants. For DBS, health technicians and field interviewers were highly correlated for HbA1c (r=0.92) and total cholesterol (r=0.89), but not for HDL cholesterol (r=0.72). The DBS results of interviewers and health technicians compared to the venous method for HbA1c (r=0.90), but did not compare well for HDL cholesterol (r=0.64-0.66) and total cholesterol (r=0.65-0.67). CONCLUSION: DBS was comparable to venous HbA1c, but not for total and HDL cholesterol. Health technicians and field interviewers had similar performance for DBS methods, except HDL cholesterol. |
Large-scale experiments and absolute detonability of methane/air mixtures
Oran ES , Gamezo VN , Zipf RK Jr . Combust Sci Technol 2015 187 324-341 The Gas Explosions Research Facility at Lake Lynn Experimental Mines was used to determine the detonability limit of methane for a 1-meter diameter tube as a function of the percent of methane in air. The measurements showed detonation limits of 5.3% (lean) and 15.6% (rich). A method for extrapolating these limits to larger systems, more relevant to coal mine tunnels, was proposed based on a simple scaling law and some empirical information on the number of cells required for a detonation to propagate in closed, open, and partially open geometries. The scaling law reproduces the measured detonation-cell sizes measured in the 1-m tube. Applying this to a tunnel the size of a coal mine produces a detonability limit less than the currently measured flammability limit for methane/air at atmospheric conditions, which raises interesting questions for detonation and combustion theory and suggests measurements in larger tubes. |
Deflagration-to-detonation transition in natural gas-air mixtures
Zipf Jr RK , Gamezo VN , Mohamed KM , Oran ES , Kessler DA . Combust Flame 2014 161 (8) 2165-2176 The gas explosion test facility (GETF) previously used to study detonability of natural gas (NG)-air mixtures was modified for studies of flame acceleration and deflagration-to-detonation transition (DDT). The 73-m-long by 1.05-m-diameter tube was equipped with 15 baffles of varying blockage ratio (BR) = 0.13, 0.25, or 0.50, placed near the closed end of the tube and spaced 1.52-m apart. The remaining part of the tube was smooth. Experiments used mixtures between 5.1% and 15.0% NG-air. Ignition was achieved in NG-air mixtures over the composition range 6.1-14.1%. After passing the 15 baffles, both flame and pressure wave velocity were more than 300 m/s over this range. Flame velocity was increasing over the range 6.2-12.8% NG-air, and it reached the sound speed in the burned gases (800-1000 m/s) over the composition range 8.0-10.8% NG-air. Pressure wave velocity was increasing over the composition range 6.1-14.1% NG-air and had reached sonic velocity over the composition range 6.2-12.6% NG-air. Shock waves with magnitude greater than 1 MPa were measured in all tests over the composition range 6.5-12.4%. DDT within the baffled section of the tube and sustained detonations beyond the baffles in the smooth part of the tube were observed over the composition range 8.0-10.8% NG-air. The observed run-up length to sonic flame velocity normalized by the tube diameter, Xru/D, ranges from 16 to 23 at BR = 0.13, 10 to 21 for BR = 0.25, and 13 to 21 for BR = 0.50. The observed run-up length to DDT normalized by the tube diameter, XDDT/D, ranges from 19 to 23 at BR = 0.13, and 16 to 23 for BR = 0.25 and 0.50. Coal mine safety regulations in the US require mine seals to resist an explosion pressure-time curve that rises instantaneously to 0.8 MPa and remains at that level for 4 s. Pressure-time curves measured in these experiments show that shock waves with near-instantaneous rise time and magnitude greater than 1 MPa can develop from weak spark ignition after passing 15 turbulence-generating obstacles in test mixtures ranging from 6.5% to 12.4% NG-air. |
Detonability of natural gas-air mixtures
Gamezo VN , Zipf Jr RK , Sapko MJ , Marchewka WP , Mohamed KM , Oran ES , Kessler DA , Weiss ES , Addis JD , Karnack FA , Sellers DD . Combust Flame 2011 159 (2) 870-881 Direct initiation experiments were carried out in a 105 cm diameter tube to study detonation properties and evaluate the detonability limits for mixtures of natural gas (NG) with air. The natural gas was primarily methane with 1.5–1.7% of ethane. A stoichiometric methane–oxygen mixture contained in a large plastic bag was used as a detonation initiator. Self-supporting detonations with velocities and pressures close to theoretical CJ values were observed in NG–air mixtures containing from 5.3% to 15.6% of NG at atmospheric pressure. These detonability limits are wider than previously measured in smaller channels, and close to the flammability limits. Detonation cell patterns recorded near the limits vary from large cells of the size of the tube to spiral traces of spin detonations. Away from the limits, detonation cell sizes decrease to about 20 cm for 10% NG, and are consistent with existing data for methane–air mixtures obtained in smaller channels. Observed cell patterns are very irregular, and contain secondary cell structures inside primary cells and fine structures inside spin traces. |
Methane-air detonation experiments at NIOSH Lake Lynn Laboratory
Zipf Jr RK , Gamezo VN , Sapko MJ , Marchewka WP , Mohamed KM , Oran ES , Kessler DA , Weiss ES , Addis JD , Karnack FA , Sellers DD . J Loss Prev Process Ind 2011 26 (2) 295-301 The methane-air detonation experiments are performed to characterize high pressure explosion processes that may occur in sealed areas of underground coal mines. The detonation tube used for these studies is 73m long, 105cm internal diameter, and closed at one end. The test gas is 97.5% methane with about 1.5% ethane, and the methane-air test mixtures varied between 4% and 19% methane by volume. Detonations were successfully initiated for mixtures containing between 5.3% and 15.5% methane. The detonations propagated with an average velocity between 1512 and 1863m/s. Average overpressures recorded behind the first shock pressure peak varied between 1.2 and 1.7MPa. The measured detonation velocities and pressures are close to their corresponding theoretical Chapman-Jouguet (CJ) detonation velocity (DCJ) and detonation pressure (PCJ). Outside of these detonability limits, failed detonations produced decaying detached shocks and flames propagating with velocities of approximately 1/2 DCJ. Cell patterns on smokefoils during detonations were very irregular and showed secondary cell structures inside primary cells. The measured width of primary cells varied between 20cm near the stoichiometry and 105cm (tube diameter) near the limits. The largest detonation cell (105cm wide and 170cm long) was recorded for the mixture containing 15.3% methane. |
Assessing blood pressure accuracy of an aneroid sphygmomanometer in a national survey environment
Ostchega Y , Prineas RJ , Nwankwo T , Zipf G . Am J Hypertens 2010 24 (3) 322-7 BACKGROUND: The "gold standard" employed for obtaining blood pressure (BP) for all the National Health and Nutrition Examination Surveys (NHANES) has been the mercury sphygmomanometer (HgS). Because of environmental concerns, there is a need to explore an alternative to HgS. METHODS: We compared the accuracy of the Welch Allyn 767 wall aneroid sphygmomanometer (AnS) to the HgS in children and adults and by BP cuff sizes. Each participant had three BP measurements per device recorded sequentially. The order of the devices and observer were random. A total of 727 individuals participating in the NHANES participated in the study. RESULTS: The mean AnS readings were not statistically significantly different from those of the HgS with the exception of systolic BP (SBP) in aged 8-17 years (mean difference 1.10, s.d. 4.87). There were no statistically significantly different by BP cuff sizes. Agreement for the prevalence of hypertension (BP ≥140 systolic or diastolic ≥90 mm Hg) was above chance (kappa = 0. 81; sensitivity = 81%; specificity = 98%) with AnS readings underestimating by 1.66% (18.33 vs. 20%, P > 0.05) compared to the HgS reading. CONCLUSIONS: With the exception of SBP in ages 8-17 years, the AnS device readings were not significantly different from HgS readings by age or BP cuff sizes selection. Agreement for hypertension classification is good. An accurate and well-calibrated AnS could therefore provide an acceptable alternative to the use of a HgS in surveys, although with appropriate caution given the 81% sensitivity with regard to hypertension thresholds that was observed.American Journal of Hypertension (2010). doi:10.1038/ajh.2010.232. |
Assessing the validity of the Omron HEM-907XL oscillometric blood pressure measurement device in a National Survey environment
Ostchega Y , Nwankwo T , Sorlie PD , Wolz M , Zipf G . J Clin Hypertens (Greenwich) 2010 12 (1) 22-8 Blood pressure (BP) readings taken by Omron HEM-907XL were compared with the results obtained using sphygmomanometer (HgS) in 509 individuals using 2002 Association for the Advancement of Medical Instrumentation (AAMI) criteria. With the exception of diastolic BP in youth ages 13 to 19 years (mean difference, -1.77 mm Hg; standard deviation, 8.65), the Omron device met the criteria. Agreement for hypertension (BP >or=140/90 mm Hg) was above chance (kappa=0.68) and, compared with HgS, Omron underestimated the prevalence of hypertension by 2.65%. The Omron and HgS measurements were highly correlated (r=0.94 for systolic BP and r=0.83 for diastolic BP). Both increased systolic and diastolic BP decreased device agreement (beta-coefficient=-0.10872, P<.0001; beta-coefficient=-0.25981, P<.0001, respectively). The Omron device meets AAMI criteria with the exception of diastolic BP in youth ages 13 to 19 years. However, Omron underestimated the prevalence of hypertension and device agreement decreases with increased systolic and diastolic BP. |
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