Independence in computable algebra

We give a sufficient condition for an algebraic structure to have a computable presentation with a computable basis and a computable presentation with no computable basis. We apply the condition to differentially closed, real closed, and difference closed fields with the relevant notions of independence. To cover these classes of structures we introduce a new technique of safe extensions that was not necessary for the previously known results of this kind. We will then apply our techniques to derive new corollaries on the number of computable presentations of these structures. The condition also implies classical and new results on vector spaces, algebraically closed fields, torsion-free abelian groups and Archimedean ordered abelian groups.Comment: 24 page

Network Structure in a Link-formation Game: An Experimental Study

Network formation is frequently modeled using link-formation games and typically present a multiplicity of Nash equilibria. Cooperative refinements - such as strong or coalitional proof Nash equilibria - have been the standard tool used for equilibrium selection in these games. Non-cooperative refinements derived from the theory of global games have shown also that, for a class of payoff functions, multiplicity of equilibria disappears when the game is perturbed by introducing small amounts of incomplete information. We conducted a laboratory study evaluating the predictive power of each of these refinements in an illustrative link-formation game. Compared with cooperative game solutions, the global game approach did significantly better at predicting the strategies played by individuals in the experiment.Networks, global games, cooperative games, equilibrium selection, experimental economics

Postactivation potentiation: predictors in NCAA Division II varsity track and field power athletes

Postactivation potentiation (PAP) is the phenomenon in which a highly trained power athlete may be able to obtain a higher rate of force development (RFD) and greater power performance following a heavy muscular loading stimulus. Research on the mechanisms of PAP indicate that it may be caused by myosin light chain (MLC) phosphorylation due to intramuscular calcium saturation during intense contraction. For PAP to be used effectively in actual performances, guidelines for its use need to be developed. This study examined the predictors of PAP, hypothesized as relative strength (REL), absolute strength (ABS), initial reactive strength index (PreRSI), and initial mean RFD (PreMRFD). Linear regressions (α = .025) were applied using those four variables for each of the outcome measures: percent change in MRFD (%MRFD), and percent change in RSI (%RSI). Means baseline values of the same four independent variables were also compared (α = .00625) between potentiated and fatigued subject groups as measured by %MRFD and %RSI. REL significantly predicted %RSI (p = .006), and ABS, PreMRFD, and PreRSI significantly predicted %MRFD (p \u3c .001). Using a cutoff value of 10% change from baseline, REL and ABS were both higher (p = .004, p = .003) in potentiated subjects with respect to %MRFD, and REL was higher (p = .005) in potentiated subjects with respect to %RSI. PAP occurs more in subjects with high REL and ABS, while subject with low REL and ABS exhibit fatigue

Public sector unions and the free-rider problem

A model of union membership is developed for State Government employees in Iowa. The union jointly produces a public and a private good using the resources from members. Employees have the choice to contribute to the union or to free-ride on the contributions of others;A probit model is used to model union membership. Membership is model as a function of wage gains, tenure, union dues and other individual characteristics;The empirical model is estimated using data on state government employees for 1980--1992. This data has very detailed wage information. The data also contains information on the dues required for union membership. Comparable worth pay plans were implemented in 1985. This provides a quasi-exogenous shock to relative wages that are not common in the public sector;A model of quits is also developed for the Iowa state employee. This model is used to develop statistical controls for potential section bias in the membership data. The model suggests that quits are negative to wages and to tenure during the early years of employment;Union membership is found to be wage elastic. In addition, membership appears to be more responsive to idiosyncratic wage gains than wage gains that accrue to all employees. The model was also used to estimate the impact that comparable worth wage increases had on membership. Union membership appears to be price inelastic when selection bias is not controlled for. Once you control for the potential bias, it appears that union membership is unitary elastic. This is consistent with an equilibrium where revenue to the union is maximized. It does not appear that other\u27s contributions are close substitutes for own contributions. This suggests that union contributions are, for the most part, private goods

Ice Nucleation by Mineral Dusts

Heterogeneous ice nucleation in the immersion mode plays a vital, yet poorly understood, role in the development of ice in mixed-phase clouds. From recent work it is thought that mineral dusts are a major, globally important source of ice-nucleating particles (INP). However, field observations to support this are sparse and the prediction of INP concentrations is challenging. This thesis expands on our current knowledge of the ice-nucleating characteristics of various components of mineral dust with the ultimate goal of being able to better predict INP concentrations globally and improve our fundamental understanding. These laboratory based experiments are then used to guide fieldwork studies and develop an interpretation of the observations. In addition to this, presented here is the development and characterisation of a new immersion mode assay for the detection of low concentrations of INP. From previous work K-feldspar is thought to be the dominant component in mineral dusts for ice nucleation. However, the quartzes have not been extensively surveyed although they make up a much larger proportion of mineral dusts than K-feldspar (in most instances). The investigation of 10 α-quartz samples show quartz to be ice active with a large variability in activity and sensitivity to time spent in water and air. The development of four new parameterisations supports evidence that K-feldspar is the dominant mineral INP in the atmosphere and we can predict field collected dust sample measurements well with the proposed K-feldspar parameterisation. We also make the first field measurements of INP at Barbados where desert dust aerosol is present which has been transported for many days after being emitted from dust sources in Africa. We show the activity of the dust to have decreased on transport across the Atlantic. Using XRD, SEM and INP modelling we attribute the deactivation to the preferential loss of the K-feldspar component on transport. The last section of this project describes the development of a 50 µL drop assay which is more sensitive to the detection of low concentrations of INP active at warm temperatures (> -15°C) and lends itself to future use in field campaigns. This instrument is novel in that it uses an infrared camera to make temperature measurements and to automatically detect freezing

Test cell set-up to enable drive-cycle testing of a variable valve actuation enabled camless diesel engine

The previous facility which was used for engine testing at Purdue\u27s Ray W. Herrick Laboratories utilized an eddy current dynamometer which is only suited for steady-state testing and throttle snaps. To better utilize a pre-existing camless diesel engine, which is is enabled via variable valve actuation, it was desired to perform transient drive-cycle tests. To accomplish this goal, a variable frequency drive AC dynamometer was required. Given that a brand new facility was constructed, the team was presented with an opportunity for ground up design of a test cell. The new test cell\u27s operation was proved out using a cammed diesel engine before moving the vairable valve actuation (VVA) enabled camless engine over. The research group\u27s best practice is to only utilize the VVA engine when collecting novel or experimental data as additional run time on this engine increases the risk of damage due to valve-to-piston interference. The goal of proving out the test cell with the cammed engine was to validate that engine operation and data collection was \u27\u27as good as or better than the previous test facility, and to solve any issues preventing the group from reaching that goal. Data acquisition results from the new test cell had noise issues which were worked out before moving over the VVA engine from the previous test cell. Fuel metering with a Cybermetrix fuel metering unit (FMU) proved to be more difficult than just plug and play, with fully functional and reliable operation taking place after the move. While the test cell\u27s room ventilation proved fully functional, additional research and work was required to hook up the conditioned combustion air system. Transient drive-cycle testing was performed with the cammed engine, and statistical analysis was performed which confirmed that the feedback speed and torque matched the reference speed and torque within EPA guidelines. This same analysis was later performed with the VVA engine and also showed capability of the VVA engine to perform repeatable drive-cycle tests. The new test cell continues to see new additions, with future work including the installation and validation of a full diesel after-treatment system which will allow for research into improving not only engine-out emissions but also tailpipe emissions through studies of the dynamic interactions between the individual exhaust components. The scope of VVA enabled diesel engine research in the Cummins Power Lab has increased from steady-state testing to transient drive-cycle testing which is more representative of how the engine is used by the end-customers

S-adenosylmethionine deficiency and demyelination. A study of metabolites of the methyl-transfer pathway in cerebrospinal fluid

Background. Subacute combined degeneration (SACD) of the spinal cord and brain has a characteristic pattern of demyelination. It is caused by deficiencies of methyl-cobalamin and methyltetrahydrofolate. A very similar pattern of demyelination is seen in acquired immunodeficiency syndrome and some histiocytic syndromes. The pathogenesis of SACD is not known, but the methyl-transfer pathway is implicated. Methods. New high-performance liquid chromatographic methods for the measurement of S-adenosylmethionine (SAM), methionine (MET) and 5-methyltetrahydrofolate (MTHF), critical metabolites in the methyl-transfer pathway, in cerebrospinal fluid (CSF) were devised and validated. Appropriate reference ranges were constructed. CSF concentrations of the metabolites were measured in children with abnormalities of the subcortical white matter due to 1) inborn errors of the methyl-transfer and transulphuration pathways, and 2) immunodeficiency and haemophagocytic syndromes. Infants with post-natal leukomalacia, who have central nervous system (CNS) macrophage activation, and children being treated with L-3,4-dihydroxyphenylalanine (L-DOPA), a compound known to require SAM for its breakdown, were also studied. Results. CSF SAM, but not MET or MTHF, was consistently reduced in those children with inborn errors and immunodeficiency or haemophagocytic syndromes at risk of developing abnormalities of subcortical white matter but not in those children with similar diseases without demyelination. When children with a low SAM and demonstrable demyelination were treated with standard therapy, previously shown to improve the neurological symptoms, SAM status was restored to normal and the white matter abnormalities were ameliorated or reversed. Infants developing leukomalacia and children treated with L-DOPA also proved to be associated with reduced CSF SAM but not MET nor MTHF. Conclusions. SAM deficiency is a critical event in the development of demyelination