Error Reduction Program

The details of a study to select, incorporate and evaluate the best available finite difference scheme to reduce numerical error in combustor performance evaluation codes are described. The combustor performance computer programs chosen were the two dimensional and three dimensional versions of Pratt & Whitney's TEACH code. The criteria used to select schemes required that the difference equations mirror the properties of the governing differential equation, be more accurate than the current hybrid difference scheme, be stable and economical, be compatible with TEACH codes, use only modest amounts of additional storage, and be relatively simple. The methods of assessment used in the selection process consisted of examination of the difference equation, evaluation of the properties of the coefficient matrix, Taylor series analysis, and performance on model problems. Five schemes from the literature and three schemes developed during the course of the study were evaluated. This effort resulted in the incorporation of a scheme in 3D-TEACH which is usuallly more accurate than the hybrid differencing method and never less accurate

Numerical simulation of gas flow and droplet motion in a wave-plate eliminator of the separator-steam-generator system in the waste-heat-utilisation complex

This paper studied the droplet transport and deposition in the turbulent flow inside a wave-plate eliminator of the waste-heat utilisation complex (WHUC). The Lagrangian discrete particle approach was used to simulate the process of liquid separation from wet steam flow. Two different models for droplet-eddy interaction were tested using data from the available literature. The tested numerical model was used to predict the WHUC performance

Clomiphene, Metformin, or Both for Infertility in the Polycystic Ovary Syndrome

Background The polycystic ovary syndrome is a common cause of infertility. Clomiphene and insulin sensitizers are used alone and in combination to induce ovulation, but it is unknown whether one approach is superior. Methods We randomly assigned 626 infertile women with the polycystic ovary syndrome to receive clomiphene citrate plus placebo, extended-release metformin plus placebo, or a combination of metformin and clomiphene for up to 6 months. Medication was discontinued when pregnancy was confirmed, and subjects were followed until delivery. Results The live-birth rate was 22.5% (47 of 209 subjects) in the clomiphene group, 7.2% (15 of 208) in the metformin group, and 26.8% (56 of 209) in the combinationtherapy group (P\u3c0.001 for metformin vs. both clomiphene and combination therapy; P=0.31 for clomiphene vs. combination therapy). Among pregnancies, the rate of multiple pregnancy was 6.0% in the clomiphene group, 0% in the metformin group, and 3.1% in the combination-therapy group. The rates of first-trimester pregnancy loss did not differ significantly among the groups. However, the conception rate among subjects who ovulated was significantly lower in the metformin group (21.7%) than in either the clomiphene group (39.5%, P=0.002) or the combinationtherapy group (46.0%, P\u3c0.001). With the exception of pregnancy complications, adverse-event rates were similar in all groups, though gastrointestinal side effects were more frequent, and vasomotor and ovulatory symptoms less frequent, in the metformin group than in the clomiphene group. Conclusions Clomiphene is superior to metformin in achieving live birth in infertile women with the polycystic ovary syndrome, although multiple birth is a complication. (ClinicalTrials.gov number, NCT00068861.

Natural Convection Heat Transfer in Enclosures With Multiple Vertical Partitions

of air or vacuum, N 2 = n + IK is the complex refractive index of the lamina material, and 9 2 is the (complex) angle of refraction, which is related to 9 t by Snell's law: N, sin #, = N 2 sin 9 2 . Since r 2l = -r i2 , the reflectance at both interfaces is equal to p = r n rf 2 , where * denotes the complex conjugate. The internal transmittance T is related to the (complex) phase change 6 by r = exp . After carefully examining the transmittance formulae of a lamina, this work shows that the geometric-optics formula may result in a significant error for a highly absorbing medium even in the incoherent limit (when interference effects are negligible). Introduction Consider the transmission of electromagnetic radiation through a lamina with smooth and parallel surfaces. In the incoherent limit when radiation coherence length is much smaller than the thickness of the lamina, the transmittance (or reflectance) may be obtained either by tracing the multiply reflected radiant power fluxes (ray-tracing method) or by separating the power flux at each interface into an outgoing component and an incoming component (net-radiation method), viz. ( where p is the reflectance at the interface and r is the internal transmittance. This formula is also called the geometric-optics formula since it is obtained without considering interference effects. For a plane wave, p equals the square of the absolute value of the complex Fresnel reflection coefficient (i.e., the ratio of the reflected electric field to the incident electric field at the interface). The Fresnel reflection coefficient is (Heavens, 1965) r\ 2 = { cos 9 2 -N 2 cos f?i JVi cos (2) N, cos 0, -N 2 cos 6*2 , . , for s -polarization ,7V, cos 9 t + N 2 cos 9 2 where 9 l is the angle of incidence, /V, = 1 is the refractive index where d is the lamina thickness and X is the wavelength in vacuum. In the coherent limit, the transmittance of a lamina may be obtained from thin-film optics (i.e., wave optics) either by tracing the reflected and transmitted waves (Airy's method) or by separating the electric fields into a forward-propagating component (forward wave) and a backward-propagating component (backward wave), viz. (Heavens, 1965; Analysis and Discussion The power transmittance at the interface between the air (or vacuum) and the medium (lamina) is where (1 + r !2 ) is the Fresnel transmission coefficient. The power transmittance at the second interface between the medium and the air can be obtained by exchanging the subscripts 1 and 2 in Eq. (6). At normal incidence, r 12 = (1 -n -('K)/(1 If both K and Im(r 21 ) are nonzero, T 2 \ =t= 1 -p. As discussed by Journal of Heat Transfer AUGUST 1997, Vol. 119/645 Copyright © 1997 by ASME Zhang The above equation is identical to Eq. (5). However, it is not a simple replacement of (1 -p) 2 in Eq. As an example, suppose the lamina is a LaA10 3 wafer of thickness d = 100 p,m. The optical constants are calculated from the Lorentian dielectric function determined by (1) and the transmittance for a LaA10 3 lamina at wavelengths from 9 to 14 p,m at normal incidence are shown in The difference between the wave-optics formula and the incoherent formula is shown in For a highly absorbing lamina (i.e., r < § 1), multiple reflections may be neglected. The transmittance obtained from Eq. (1), when multiple reflections are negligible, is (1 -pfr. The transmittance calculated from Eq. (8) for T < 1 is where the last expression is for normal incidence only. Eq. Concluding Remarks By inspecting the energy balance at the second interface, this work reveals an implicit assumption associated with Eq. Certain important applications require the determination of transmittance below 10~4. Examples are in the characterization of attenuation filters, bandpass filters, and materials with strong absorption bands Acknowledgments This work has been supported by the University of Florida through a start-up fund and an Interdisciplinary Research Initiative award. / Vol. 119, AUGUST 1997 Transactions of the ASME A. A., 1994, "Modelling of the Reflectance of Silicon," Infrared Physics and Technology, Vol. 35, pp. 701 -708. Frenkel, A" and Zhang, Z. M" 1994, "Broadband High Optical Density Filters in the Infrared," Optics Letters, Vol. 19, pp. 1495-1497 Gentile, T. R., Frenkel, A" Migdall, A. L., and Zhang, Z. M" 1995, "Neutral Density Filter Measurements at the National Institute of Standards and Technology," Spectrophotometry, Luminescence and Colour; Science and Compliance, C. Burgess and D. G. Jones, eds., Elsevier, Amsterdam, The Netherlands, pp. 129-139. Grossman, E. N" and McDonald, D. G" 1995, "Partially Coherent Transmittance of Dielectric Lamellae," Optical Engineering, Vol. 34, pp. 1289-1295. Heavens, O. S., 1965, Optical Properties of Thin Solid Films, Dover Publications, Inc., New York, chap. 4, pp. 46-95. Knittl, Z" 1976, Optical of Thin Films, John Wiley & Sons, Inc., NY, pp. 203-204. Salzberg, B., 1948, "A Note on the Significance of Power Reflection," American Journal of Physics, Vol. 16, pp. 444-446. Siegel, R" and Howell, J. R., 1992, Thermal Radiation Heat Transfer, 3rd ed" Hemisphere Publishing Corp., Washington D.C., chap. 4, p. 120, and chap. 18, pp. 928-930. Yeh, P., 1988, Optical Waves in Layered Media, John Wiley & Sons, Inc., New York, chap. 4, pp. 83-101. Zhang, Z. M., 199

Smoking cessation and bronchial epithelial remodelling in COPD: a cross-sectional study

<p>Abstract</p> <p>Background</p> <p>Chronic Obstructive Pulmonary Disease (COPD) is associated with bronchial epithelial changes, including squamous cell metaplasia and goblet cell hyperplasia. These features are partially attributed to activation of the epidermal growth factor receptor (EGFR). Whereas smoking cessation reduces respiratory symptoms and lung function decline in COPD, inflammation persists. We determined epithelial proliferation and composition in bronchial biopsies from current and ex-smokers with COPD, and its relation to duration of smoking cessation.</p> <p>Methods</p> <p>114 COPD patients were studied cross-sectionally: 99 males/15 females, age 62 ± 8 years, median 42 pack-years, no corticosteroids, current (n = 72) or ex-smokers (n = 42, median cessation duration 3.5 years), postbronchodilator FEV₁63 ± 9% predicted. Squamous cell metaplasia (%), goblet cell (PAS/Alcian Blue⁺) area (%), proliferating (Ki-67⁺) cell numbers (/mm basement membrane), and EGFR expression (%) were measured in intact epithelium of bronchial biopsies.</p> <p>Results</p> <p>Ex-smokers with COPD had significantly less epithelial squamous cell metaplasia, proliferating cell numbers, and a trend towards reduced goblet cell area than current smokers with COPD (p = 0.025, p = 0.001, p = 0.081, respectively), but no significant difference in EGFR expression. Epithelial features were not different between short-term quitters (<3.5 years) and current smokers. Long-term quitters (≥3.5 years) had less goblet cell area than both current smokers and short-term quitters (medians: 7.9% vs. 14.4%, p = 0.005; 7.9% vs. 13.5%, p = 0.008; respectively), and less proliferating cell numbers than current smokers (2.8% vs. 18.6%, p < 0.001).</p> <p>Conclusion</p> <p>Ex-smokers with COPD had less bronchial epithelial remodelling than current smokers, which was only observed after long-term smoking cessation (>3.5 years).</p> <p>Trial registration</p> <p>NCT00158847</p

Multidrug resistance-associated protein-1 (MRP1) genetic variants, MRP1 protein levels and severity of COPD

<p>Abstract</p> <p>Background</p> <p>Multidrug resistance-associated protein-1 (MRP1) protects against oxidative stress and toxic compounds generated by cigarette smoking, which is the main risk factor for chronic obstructive pulmonary disease (COPD). We have previously shown that single nucleotide polymorphisms (SNPs) in <it>MRP1 </it>significantly associate with level of FEV₁in two independent population based cohorts. The aim of our study was to assess the associations of <it>MRP1 </it>SNPs with FEV₁level, MRP1 protein levels and inflammatory markers in bronchial biopsies and sputum of COPD patients.</p> <p>Methods</p> <p>Five SNPs (rs212093, rs4148382, rs504348, rs4781699, rs35621) in <it>MRP1 </it>were genotyped in 110 COPD patients. The effects of <it>MRP1 </it>SNPs were analyzed using linear regression models.</p> <p>Results</p> <p>One SNP, rs212093 was significantly associated with a higher FEV₁level and less airway wall inflammation. Another SNP, rs4148382 was significantly associated with a lower FEV₁level, higher number of inflammatory cells in induced sputum and with a higher MRP1 protein level in bronchial biopsies.</p> <p>Conclusions</p> <p>This is the first study linking <it>MRP1 </it>SNPs with lung function and inflammatory markers in COPD patients, suggesting a role of <it>MRP1 </it>SNPs in the severity of COPD in addition to their association with MRP1 protein level in bronchial biopsies.</p

Development and application of bivariate 2D-EMD for the analysis of instantaneous flow structures and cycle-to-cycle variations of in-cylinder flow

International audienceThe bivariate two dimensional empirical mode decomposition (Bivariate 2D-EMD) is extended to estimate the turbulent fluctuations and to identify cycle-to-cycle variations (CCV) of in-cylinder flow. The Bivariate 2D-EMD is an adaptive approach that is not restricted by statistical convergence criterion, hence it can be used for analyzing the nonlinear and non-stationary phenomena. The methodology is applied to a high-speed PIV dataset that measures the velocity field within the tumble symmetry plane of an optically accessible engine. The instantaneous velocity field is decomposed into a finite number of 2D spatial modes. Based on energy considerations, the in-cylinder flow large-scale organized motion is separated from turbulent fluctuations. This study is focused on the second half of the compression stroke. For most of the cycles, the maximum of turbulent fluctuations is located between 50 and 30 crank angle degrees before top dead center (TDC). In regards to the phase-averaged velocity field, the contribution of CCV to the fluctuating kinetic energy is approximately 55% near TDC

Three-Armed Trials Including Placebo and No-Treatment Groups May Be Subject to Publication Bias: Systematic Review

Background: It has been argued that placebos may not have important clinical impacts in general. However, there is increasing evidence of a publication bias among trials published in journals. Therefore, we explored the potential for publication bias in randomized trials with active treatment, placebo, and no-treatment groups. Methods: Three-armed randomized trials of acupuncture, acupoint stimulation, and transcutaneous electrical stimulation were obtained from electronic databases. Effect sizes between treatment and placebo groups were calculated for treatment effect, and effect sizes between placebo and no-treatment groups were calculated for placebo effect. All data were then analyzed for publication bias. Results: For the treatment effect, small trials with fewer than 100 patients per arm showed more benefits than large trials with at least 100 patients per arm in acupuncture and acupoint stimulation. For the placebo effect, no differences were found between large and small trials. Further analyses showed that the treatment effect in acupuncture and acupoint stimulation may be subject to publication bias because study design and any known factors of heterogeneity were not associated with the small study effects. In the simulation, the magnitude of the placebo effect was smaller than that calculated after considering publication bias. Conclusions: Randomized three-armed trials, which are necessary for estimating the placebo effect, may be subject t