The Effects of Remedial Mathematics on the Learning of Economics: A Natural Experiment.

This paper examines the effects of remedial mathematics on performance in university-level economics courses using a natural experiment. We study exam results prior and subsequent to the implementation of a remedial mathematics course that was compulsory for a sub-set of students and unavailable for the others, controlling for background variables. We find that, consistent with previous studies, the level of and performance in secondary-school mathematics has strong predictive power on students’ performance at university-level economics. However, the evidence for a positive effect of remedial mathematics on student performance is relatively weak and is limited to a few sub-groups of students

Co-authorship in economic history and economics: are we any different?

Over the last six decades there has been less co-authorship in leading economic history journals than in leading general economics journals. There has also been a strong, monotonic increase in co-authorship in economic history journals that roughly parallels general economics journals but sharply differs from leading history journals. Increased co-authorship cannot be explained by increasing use of econometrics or large data sets; rather, it is likely due to common changes in incentives facing economic historians and economists. Finally, co-authorships in economic history are more likely to be formed of individuals of different seniority compared to economics generally

Furnace and Heat Recovery Area Design and Analysis for Conceptual Design of Supercritical O2-Based PC Boiler

The objective of the furnace and heat recovery area design and analysis task of the Conceptual Design of Supercritical Oxygen-Based PC Boiler study is to optimize the location and design of the furnace, burners, over-fire gas ports, and internal radiant surfaces. The furnace and heat recovery area were designed and analyzed using the FW-FIRE, Siemens, and HEATEX computer programs. The furnace is designed with opposed wall-firing burners and over-fire air ports. Water is circulated in the furnace by forced circulation to the waterwalls at the periphery and divisional wall panels within the furnace. Compared to the air-fired furnace, the oxygen-fired furnace requires only 65% of the surface area and 45% of the volume. Two oxygen-fired designs were simulated: (1) with cryogenic air separation unit (ASU) and (2) with oxygen ion transport membrane (OITM). The maximum wall heat flux in the oxygen-fired furnace is more than double that of the air-fired furnace due to the higher flame temperature and higher H{sub 2}O and CO{sub 2} concentrations. The coal burnout for the oxygen-fired case is 100% due to a 500 F higher furnace temperature and higher concentration of O{sub 2}. Because of the higher furnace wall temperature of the oxygen-fired case compared to the air-fired case, furnace water wall material was upgraded from T2 to T92. Compared to the air-fired heat recovery area (HRA), the oxygen-fired HRA total heat transfer surface is 35% less for the cryogenic design and 13% less for the OITM design due to more heat being absorbed in the oxygen-fired furnace and the greater molecular weight of the oxygen-fired flue gas. The HRA tube materials and wall thickness are nearly the same for the air-fired and oxygen-fired design since the flue gas and water/steam temperature profiles encountered by the heat transfer banks are similar

Economic Analysis for Conceptual Design of Supercritical O2-Based PC Boiler

This report determines the capital and operating costs of two different oxygen-based, pulverized coal-fired (PC) power plants and compares their economics to that of a comparable, air-based PC plant. Rather than combust their coal with air, the oxygen-based plants use oxygen to facilitate capture/removal of the plant CO{sub 2} for transport by pipeline to a sequestering site. To provide a consistent comparison of technologies, all three plants analyzed herein operate with the same coal (Illinois No 6), the same site conditions, and the same supercritical pressure steam turbine (459 MWe). In the first oxygen-based plant, the pulverized coal-fired boiler operates with oxygen supplied by a conventional, cryogenic air separation unit, whereas, in the second oxygen-based plant, the oxygen is supplied by an oxygen ion transport membrane. In both oxygen-based plants a portion of the boiler exhaust gas, which is primarily CO{sub 2}, is recirculated back to the boiler to control the combustion temperature, and the balance of the flue gas undergoes drying and compression to pipeline pressure; for consistency, both plants operate with similar combustion temperatures and utilize the same CO{sub 2} processing technologies. The capital and operating costs of the pulverized coal-fired boilers required by the three different plants were estimated by Foster Wheeler and the balance of plant costs were budget priced using published data together with vendor supplied quotations. The cost of electricity produced by each of the plants was determined and oxygen-based plant CO{sub 2} mitigation costs were calculated and compared to each other as well as to values published for some alternative CO{sub 2} capture technologies

Ammonia-Free NOx Control System

Research is being conducted under United States Department of Energy (DOE) Contract DEFC26-03NT41865 to develop a new technology to achieve very low levels of NOx emissions from pulverized coal fired boiler systems by employing a novel system level integration between the PC combustion process and the catalytic NOx reduction with CO present in the combustion flue gas. The combustor design and operating conditions will be optimized to achieve atypical flue gas conditions. This approach will not only suppress NOx generation during combustion but also further reduce NOx over a downstream catalytic reactor that does not require addition of an external reductant, such as ammonia