Liner environment effects study

The Liner Environment Effects Study Program is aimed at establishing a broad heat transfer data base under controlled experimental conditions by quantifying the effects of the combustion system conditions on the combustor liner thermal loading and on the flame radiation characteristics. Five liner concepts spanning the spectrum of liner design technology from the very simple to the most advanced concepts are investigated. These concepts comprise an uncooled liner, a conventional film cooled liner, an impingement/film cooled liner, a laser drilled liner approaching the concept of a porous wall, and a siliconized silicon carbide ceramic liner. Effect of fuel type is covered by using fuels containing 11.8, 12.8, and 14% hydrogen. Tests at 100, 200, and 300 psia provide a basis for evaluating the effect of pressure on the heat transfer. The effects of the atomization quality and spray characteristics are examined by varying the fuel spray Sauter mean diameter and the spray angle. Additional varied parameters include reference velocity, a wide range of equivalence ratio, cooling flow rate, coolant temperature and the velocity of the coolant stream on the backside of the liner

Experimental study of the effect of cycle pressure on lean combustion emissions

Experiments were conducted in which a stream of premixed propane and air was burned under conditions representative of gas turbine operation. Emissions of NOx, CO, and unburned hydrocarbons (UHC) were measured over a range of combustor inlet temperature, pressure, and residence time at equivalence ratios from 0.7 down to the lean stability limit. At an inlet temperature of 600 K, observed NOx levels dropped markedly with decreasing pressure for pressures below 20 atm. The NOx levels are proportional to combustor residence time and formation rates were principally a function of adiabatic flame temperature. For adiabatic flame temperatures of 2050 K and higher, CO reached chemical equilibrium within 2 msec. Unburned hydrocarbon species dropped to a negligible level within 2 msec regardless of inlet temperature, pressure, or equivalence ratio. For a combustor residence time of 2.5 msec, combustion inefficiency became less than 0.01% at an adiabatic flame temperature of 2050 K. The maximum combustion inefficiency observed was on the order of 1% and corresponded to conditions near the lean stability limit. Using a perforated plate flameholder, this limit is well represented by the condition of 1800 K adiabatic flame temperature

Experimental study of the effects of flameholder geometry on emissions and performance of lean premixed combustors

Emissions of NOx, CO, and unburned hydrocarbons (UHC) are reported for a lean premixed propane-air system at inlet conditions of 800K and 1MPa using twelve flameholder designs. The flameholders tested represent six design concepts with two values of blockage for each concept. Data were obtained at reference velocities of 35 m/s, 25 m/s and 20 m/s at combustor stations 10 cm and 30 cm downstream of the flameholders. Flameholder pressure drop was found to be a principal determinant of emissions performance. Designs producing larger pressure drops also produced less NOx, CO, and UHC emissions. The lean stability limit equivalence ratio was found to be approximately 0.35 for all designs. Flashback velocities (axial components in the flameholder passages) varied between 30 m/s and 40 m/s. A perforated plate flameholder was operated with a velocity as low as 23 m/s through the perforations at equivalence ratio 0.7 without producing flashback

Technical Efficiency in Agricultural Production and Its Determinants : An Exploratory Study at the District Level

Given the importance of agriculture to the well being of a large percentage of Indias population, it becomes important to study how improvements can be made in the productivity of this sector. This study attempts to estimate the technical efficiency a measure of how well inputs are being used towards producing output of about 250 Indian districts in 1990-91. It employs the stochastic frontier function methodology. The results indicate that (i) the land elasticity is the highest followed by fertilizer; (ii) the mean efficiency of raising agricultural output is 79 per cent and therefore there is a scope for increasing output by 21 per cent without additional resources; (iii) states such as Madhya Pradesh, Uttar Pradesh, and Rajasthan have the largest number of districts with below average TE and they stand to gain the most from policy interventions towards improving technical efficiency. The results further indicate that health, education, and infrastructure are powerful drivers of efficiency at the district level and the relative importance of the determinants of efficiency across districts depends greatly on environmental factors, such as agro-climatic zones, technological factors, and crop mix. The results highlight the need for developing policy strategies at a more localized level.agriculture, technical efficiency, stochastic frontier function, India

Effects of flameholder geometry on emissions and performance of lean premixed combustors

Emission levels and performance of twelve flameholder designs were investigated in a lean, premixed propane-air system at inlet conditions of 800K and 10 atm. The flameholder tested represents six design concepts with two values of blockage for each concept. The design concept consists of the following geometries: perforated plate, wire grid, single cone, multiple cone, vee gutter and swirl cone. Measurements were made at reference velocities of 35 m/s, 25 m/s and 20 m/s at combustor stations 10 cm and 30 cm downstream of the flameholder

Premix fuels study applicable to duct burner conditions for a variable cycle engine

Emission levels and performance of a premixing Jet-A/air duct burner were measured at reference conditions representative of take-off and cruise for a variable cycle engine. In a parametric variation sequence of tests, data were obtained at inlet temperatures of 400, 500 and 600K at equivalence ratios varying from 0.9 to the lean stability limit. Ignition was achieved at all the reference conditions although the CO levels were very high. Significant nonuniformity across the combustor was observed for the emissions at the take-off condition. At a reference Mach number of 0.117 and an inlet temperature of 600K, corresponding to a simulated cruise condition, the NOx emission level was approximately 1 gm/kg-fuel

Task-driven Prompt Evolution for Foundation Models

Promptable foundation models, particularly Segment Anything Model (SAM), have emerged as a promising alternative to the traditional task-specific supervised learning for image segmentation. However, many evaluation studies have found that their performance on medical imaging modalities to be underwhelming compared to conventional deep learning methods. In the world of large pre-trained language and vision-language models, learning prompt from downstream tasks has achieved considerable success in improving performance. In this work, we propose a plug-and-play Prompt Optimization Technique for foundation models like SAM (SAMPOT) that utilizes the downstream segmentation task to optimize the human-provided prompt to obtain improved performance. We demonstrate the utility of SAMPOT on lung segmentation in chest X-ray images and obtain an improvement on a significant number of cases ($\sim75\%$) over human-provided initial prompts. We hope this work will lead to further investigations in the nascent field of automatic visual prompt-tuning

Latitudinal trends in O<SUB>3</SUB>, CO, CH<SUB>4</SUB> and SF<SUB>6</SUB> over the Indian Ocean during the INDOEX IFP-1999 ship cruise

Surface measurements of ozone (O3), carbon monoxide (CO), methane (CH4) and sulfur hexafluoride (SF6) were made over the Arabian Sea and the Indian Ocean during the INDOEX field experiment in January- March 1999 covering the latitude range from 17&#176;N to 20&#176;S. Observations show decreasing trends in all these trace gases from the Indian coastal region to the open Indian Ocean. Ozone with a lifetime of few days, shortest among the species presented here, shows large variations while SF6, which has relatively longer lifetime, shows smaller variations. Ozone also shows clearly the effect of ITCZ and its movement. These observations show higher ozone near the Indian coastal region in January 1999 than in March 1999 and also compared to the observed ozone during the INDOEX-1998 cruise. This is believed to be due to strong anti-cyclonic conditions in January 1999 bringing more polluted air from the Indian continent. A decrease in the latitudinal gradient in CH4 was observed in 1999 compared to that in 1998 in the same region, indicating slower growth rate in 1998-1999 period

Population dynamics and stock assessment of Delegoa threadfin bream, Nemipterus bipunctatus (Nemipteridae), from the Wadge Bank, South India

Fishery, population characteristics and stock estimates of Nemipterus bipunctatus were studied during June 2015 to May 2016 from Wadge Bank, South India. This region is characterised by rich biodiversity and has a conducive influence of the Indian Ocean and Arabian Sea. The asymptotic length (L?), growth coefficient (K) and arbitrary origin of growth (t0) were estimated as 30.5 cm, 0.85/year and 0.18 respectively. The mortality parameters, total mortality rate (Z), fishing mortality rate and natural mortality rate (M) were estimated as 2.20, 0.95 and 1.25 respectively. Exploitation ratio (E) was found to be 0.57 which showed marginal over exploitation of the species at Wadge Bank. This species has two recruitment seasons, one major season from October to December and another minor season in August. The length structured Virtual population analysis revealed heavy fishing pressure on the length group 24 to 28 cm and hence the delegoa threadfin bream was not found to suffer due to recruitment overfishing in Wadge Bank. Estimated total stock, Maximum Sustainable Yield (MSY) and annual catch were 5625.9348 tonnes, 1935.321t, 2419.152t respectively. Present level of Exploitation rate (U) and Exploitation ratio (F/Z) were estimated to be 0.43 and 0.57 respectively. The study infers the cod end mesh size of the trawls operated at Wadge Bank coast has to be increase from 10 to 25 mm to increase the yield per recruit, the effort could also be maintained as the exploitation ratio of 0.50 to have maximum yield per recruit. The study suggests reducing the present level of effort by 8 percent may be needed to sustain the stock of N. bipunctatus in Wadge Bank, South Indi

Infinities of stable periodic orbits in systems of coupled oscillators

We consider the dynamical behavior of coupled oscillators with robust heteroclinic cycles between saddles that may be periodic or chaotic. We differentiate attracting cycles into types that we call phase resetting and free running depending on whether the cycle approaches a given saddle along one or many trajectories. At loss of stability of attracting cycling, we show in a phase-resetting example the existence of an infinite family of stable periodic orbits that accumulate on the cycling, whereas for a free-running example loss of stability of the cycling gives rise to a single quasiperiodic or chaotic attractor