Design and fabrication of a tin-sulfide annealing furnace

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 22-23).A furnace was designed and its heat transfer properties were analyzed for use in annealing thin-film tins-ulfide solar cells. Tin sulfide has been explored as an earth abundant solar cell material, and the furnace was developed to test the properties of annealed tin-sulfide thin films. Annealing is a highly temperature and time dependent process so the furnace must be able to reach the temperature to be tested quickly, maintain that temperature and once finished, cool down quickly. The furnace is composed of a quartz tube with two heated zones, both heated with nichrome wire and cooled with fans. The two zones were designed to reach temperatures of 600 C and 200 C and to be cooled at a rate of 10 C per minute.by Raymond Lewis.S.B

Heuristics for batching jobs under weighted average completion time

Batching problems are machine scheduling problems, where a set of jobs with given processing requirements has to be scheduled on a single machine. The set of jobs has to be partitioned into subsets to form a sequence of batches. A batch combines jobs to run jointly, and each job\u27s completion time is defined to be the completion time of the entire batch. For a batching problem, it is also assumed that when each batch is scheduled, it requires a setup time. One seeks to find a schedule that minimizes the total weighted completion time; This problem is NP-complete, but the problem can be solved efficiently in O(n log (n)) time if the order of the jobs is given. This is accomplished through a non-trivial reduction to on-line matrix searching in a totally monotone array. An implementation of this algorithm is part of the thesis work; To remove the requirement of a fixed order and thus to solve the original NP-complete batching problem, the space of permutations is searched using a genetic algorithm technique. The implementation uses a library of object-oriented functions, GAlib, to implement genetic algorithms. This highly versatile library was written by Mathew Wall of MIT; The thesis also seeks to find techniques to obtain an upper bound, which can be used to measure the quality of the solutions found by the heuristic

High compression ratio turbo gasoline engine operation using alcohol enhancement

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.Page 62 blank. Cataloged from PDF version of thesis.Includes bibliographical references (page 61).Gasoline - ethanol blends were explored as a strategy to mitigate engine knock, a phenomena in spark ignition engine combustion when a portion of the end gas is compressed to the point of spontaneous auto-ignition. This auto-ignition is dangerous to the operation of an internal combustion engine, as it can severely damage engine components. As engine designers are trying to improve the efficiency of the internal combustion engine, engine knock is a key limiting factor in engine design. Two methods have been used to limit engine knock that will be considered here; retarding the spark timing and addition of additives to reduce the tendency of the fuel mixture to knock. Both have drawbacks. Retarding spark reduces the engine efficiency and additives typically lower the heating value of the fuel, requiring more fuel for a given operating point. To study this problem a turbocharged engine was tested with a variety of combinations of gasoline and ethanol, an additive with very good anti-knock abilities. Pressure was recorded and GT Power simulations were used to determine the temperature within the cylinder. An effective octane number was calculated to measure the ability of the fuel to resist knock. Effective octane numbers varied from 91 for UTG91 to 111 for E25, respectively. Engine simulations were used to extrapolate to points that couldn't be tested in the experimental setup and generate performance maps which could be used to predict how the engine would act inside of a vehicle. It was found that increasing the compression ratio from 9.2 to 13.5 leads to a 7% relative increase in part load efficiency. When applied in a vehicle this leads to a 2-6% increase in miles per gallon of gasoline consumption depending on the drive cycle used. Miles per gallon of ethanol used were significantly higher than gasoline; 141 miles per gallon of ethanol was the lowest mileage over all cycles studied.by Raymond Lewis.S.M

A Pasture System for You

This publication describes the management of a series of tame pastures (with or without native range) for maximum forage production. Information is provided on the productivity of tame grasses, grazing systems, seasonal pastures, special purpose grasses, and pasture alternatives

A Pasture System for You

Guide to pasture systems discusses productivity of tame grasses, grazing systems, and seasonal pastures. Includes tables for the minimum heights of pasture species for initiation and terminating grazing and two suggested pasture systems

A Numerical Investigation of the Local Ocean Response to Westerly Wind Burst Forcing in the Western Equatorial Pacific

Numerical simulations of the local equatorial ocean response to idealized westerly wind burst (WWB) forcing are described. In particular, the authors examine the development and evolution of the subsurface westward jet (SSWJ) that has been observed to accompany these wind events. This westward current is interpreted as the signature of equatorial waves that accompany the downwelling and upwelling that occurs along the edges of the wind forcing region. Some important features of the SSWJ include maximum intensity toward the eastern edge of the forcing region, a time lag between the wind forcing and peak SSWJ development, and an eastward spreading of the SSWJ with time. The effect of wind burst zonal profile, magnitude, duration, and fetch on the SSWJ are explored. The response of an initially resting ocean to WWB forcing is compared with that for model oceans that are spun up with annual-mean surface fluxes and monthly varying fluxes. It is demonstrated that the gross features of the response for the spun up simulations can be well approximated by adding the background zonal current structure prior to the introduction of the wind burst to the initially resting ocean current response to the WWB. This result suggests that the zonal current structure that is present prior to the commencement of WWB forcing plays a key role in determining whether or not a SSWJ will develop

Computer model to simulate testing at the National Transonic Facility

A computer model has been developed to simulate the processes involved in the operation of the National Transonic Facility (NTF), a large cryogenic wind tunnel at the Langley Research Center. The simulation was verified by comparing the simulated results with previously acquired data from three experimental wind tunnel test programs in the NTF. The comparisons suggest that the computer model simulates reasonably well the processes that determine the liquid nitrogen (LN2) consumption, electrical consumption, fan-on time, and the test time required to complete a test plan at the NTF. From these limited comparisons, it appears that the results from the simulation model are generally within about 10 percent of the actual NTF test results. The use of actual data acquisition times in the simulation produced better estimates of the LN2 usage, as expected. Additional comparisons are needed to refine the model constants. The model will typically produce optimistic results since the times and rates included in the model are typically the optimum values. Any deviation from the optimum values will lead to longer times or increased LN2 and electrical consumption for the proposed test plan. Computer code operating instructions and listings of sample input and output files have been included

Likert Items: Should(n’t) We Really Care?

One of the controversial methodological topics in the social and behavioral sciences is the (ab)use of Likert Scale items, Likert-type items and ranked ordered response categories. The debate is whether parametric tests can be legitimately conducted on technically ordinal response categories that are represented with numbers. Participants answered survey questions on moral disengagement, where we changed the intervals of seven response categories and tested whether assigning numbers made any difference in two separate studies. The results showed that participants’ ratings were not significantly different with or without numbers. Participants tend to covertly superimpose numbers where none were provided. Also, there were no significant interactions between assignment of numbers and ‘intervalness’. However, ratings were significantly different between two key interval groups. Knowing the assumptions of respondents to these Likert items even without numbers could inform researchers especially if parametric tests are to be conducted

Live to cheat another day: bacterial dormancy facilitates the social exploitation of beta-lactamases

The breakdown of antibiotics by β-lactamases may be cooperative, since resistant cells can detoxify their environment and facilitate the growth of susceptible neighbours. However, previous studies of this phenomenon have used artificial bacterial vectors or engineered bacteria to increase the secretion of β-lactamases from cells. Here, we investigated whether a broad-spectrum β-lactamase gene carried by a naturally occurring plasmid (pCT) is cooperative under a range of conditions. In ordinary batch culture on solid media, there was little or no evidence that resistant bacteria could protect susceptible cells from ampicillin, although resistant colonies could locally detoxify this growth medium. However, when susceptible cells were inoculated at high densities, late-appearing phenotypically susceptible bacteria grew in the vicinity of resistant colonies. We infer that persisters, cells that have survived antibiotics by undergoing a period of dormancy, founded these satellite colonies. The number of persister colonies was positively correlated with the density of resistant colonies and increased as antibiotic concentrations decreased. We argue that detoxification can be cooperative under a limited range of conditions: if the toxins are bacteriostatic rather than bacteridical; or if susceptible cells invade communities after resistant bacteria; or if dormancy allows susceptible cells to avoid bactericides. Resistance and tolerance were previously thought to be independent solutions for surviving antibiotics. Here, we show that these are interacting strategies: the presence of bacteria adopting one solution can have substantial effects on the fitness of their neighbours