Dynamic Model Averaging for Practitioners in Economics and Finance: The eDMA Package

Raftery, Karny, and Ettler (2010) introduce an estimation technique, which they refer to as Dynamic Model Averaging (DMA). In their application, DMA is used to predict the output strip thickness for a cold rolling mill, where the output is measured with a time delay. Recently, DMA has also shown to be useful in macroeconomic and financial applications. In this paper, we present the eDMA package for DMA estimation implemented in R. The eDMA package is especially suited for practitioners in economics and finance, where typically a large number of predictors are available. Our implementation is up to 133 times faster then a standard implementation using a single-core CPU. Thus, with the help of this package, practitioners are able to perform DMA on a standard PC without resorting to large clusters, which are not easily available to all researchers. We demonstrate the usefulness of this package through simulation experiments and an empirical application using quarterly U.S. inflation data.Comment: 21 pages, 5 figures, 2 table

Dynamic mechanical analysis and organization/storage of data for polymetric materials

Dynamic mechanical analysis was performed on a variety of temperature resistant polymers and composite resin matrices. Data on glass transition temperatures and degree of cure attained were derived. In addition a laboratory based computer system was installed and data base set up to allow entry of composite data. The laboratory CPU termed TYCHO is based on a DEC PDP 11/44 CPU with a Datatrieve relational data base. The function of TYCHO is integration of chemical laboratory analytical instrumentation and storage of chemical structures for modeling of new polymeric structures and compound

The Mutual Interaction Between Population III Stars and Self-Annihilating Dark Matter

We use cosmological simulations of high-redshift minihalos to investigate the effect of dark matter annihilation (DMA) on the collapse of primordial gas. We numerically investigate the evolution of the gas as it assembles in a Population III stellar disk. We find that when DMA effects are neglected, the disk undergoes multiple fragmentation events beginning at ~ 500 yr after the appearance of the first protostar. On the other hand, DMA heating and ionization of the gas speeds the initial collapse of gas to protostellar densities and also affects the stability of the developing disk against fragmentation, depending on the DM distribution. We compare the evolution when we model the DM density with an analytical DM profile which remains centrally peaked, and when we simulate the DM profile using N-body particles (the 'live' DM halo). When utilizing the analytical DM profile, DMA suppresses disk fragmentation for ~ 3500 yr after the first protostar forms, in agreement with earlier work. However, when using a 'live' DM halo, the central DM density peak is gradually flattened due to the mutual interaction between the DM and the rotating gaseous disk, reducing the effects of DMA on the gas, and enabling secondary protostars of mass ~ 1 M_sol to be formed within ~ 900 yr. These simulations demonstrate that DMA is ineffective in suppressing gas collapse and subsequent fragmentation, rendering the formation of long-lived dark stars unlikely. However, DMA effects may still be significant in the early collapse and disk formation phase of primordial gas evolution.Comment: 17 pages, 11 figures, to appear in MNRA

PREVENTION AND CONTROL OF DIMETHYLAMINE VAPORS EMISSION: HERBICIDE PRODUCTION PLANT

The widely used herbicide, dimethylamine salt of 2,4-dichlorophenoxy acetic acid (2,4-D-DMA), is usually prepared by mixing a dimethylamine (DMA) aqueous solution with a solid 2,4-dichlorophenoxy acetic acid (2,4-D). The vapors of the both, reactants and products, are potentially hazardous for the environment. The contribution of DMA vapors in overall pollution from this process is most significant, concerning vapor pressures data of these pollutants. Therefore, the control of the air pollution in the manufacture and handling of methylamines is very important. Within this paper, the optimal air pollution control system in preparation of 2,4-D-DMA was developed for the pesticides manufacturing industry. This study employed the simple pollution prevention concept to reduce the emission of DMA vapors at the source. The investigations were performed on the pilot plant scale. To reduce the emission of DMA vapors, the effluent gases from the herbicide preparation zone were passed through the packed bed scrubber (water - scrubbing medium), and the catalytic reactor in sequence. The end result is a substantially improved air quality in the working area, as well as in the urbanized areas located near the chemical plant

Heat Generation in the Railroad Bearing Thermoplastic Elastomer Suspension Element

The main purpose of this ongoing study is to investigate the effect of heat generation within a railroad thermoplastic elastomer suspension element on the thermal behavior of the railroad bearing assembly. Specifically, the purpose of this project is to quantify the heat generated by cyclic loading of the elastomer suspension element as a function of load amplitude, loading frequency, and operating temperature. The contribution of the elastomer pad to the system energy balance is modeled using data from dynamic mechanical analysis (DMA) of the specific materials in use for that part. DMA is a technique that is commonly used to characterize material properties as a function of temperature, time, frequency, stress, atmosphere or a combination of these parameters. DMA tests were run on samples of pad material prepared by three different processes: injection molded coupons, transfer molded coupons, and parts machined from an actual pad. The results provided a full characterization of the elastic deformation (Energy Storage) and viscous dissipation (Energy Dissipation) behavior of the material as a function of loading frequency, and temperature. These results show that the commonly used thermoplastic elastomer does generate heat under cyclic loading, though the frequency which produces peak heat output is outside the range of common loading frequency in rail service. These results can be combined with a stress analysis and service load measurements to estimate internally generated heat and, thus, enable a refined model for the evolution of bearing temperature during operation

Effect of internal moisture content on the TG values of CFRP rods

DMA tests are used for the material charaterisation of CFRP tendons for civil engineering applications and to assess the high temperature behavior of CFRP prestressed structures by measuring the glass transition temperature Tg. The glass transition temperature is sensitive to the moisture content of the CFRP tendons and standard test methods (e.g. ASTM D7028 (ASTM 2007)) have not yet qualitatively addressed the effect of small moisture content variations from environmental conditions in the Tg values. The effect of the internal moisture content on the Tg values of two CFRP rods with different diameters and manufacturing process is evaluated. Lab conditioned specimens with varying drying time (9, 15, 36 and 210 days) and thus moisture content are tested to study the effect of small lab conditions variations in the glass transition temperature and the sensitivity of the DMA testing. Exposed specimens at 60°C for roughly 3 years are also investigated to record effect of greater moisture absorption on the Tg values. Two heating runs were conducted for every test to differentiate postcuring effects and mass weight measurements were recorded before and after each heating run. A linear relationship between the mass loss of the specimens due to drying at vacuum and during the heating runs with the glass transition temperature Tg was observed. Post-curing effects could not be clarified even for the dry specimens. The exposed specimens showed a reduction in Tg of 38°C that was reversible after drying. It is recommended that the use of Tg values to infer the degree of curing should be carried out on dry specimens.SACAC Ltd, Onassis Foundatio

Hysteresis Heating of Railroad Bearing Thermoplastic Elastomer Suspension Element

Thermoplastic elastomers (TPE’s) are increasingly being used in rail service in load damping applications. They are superior to traditional elastomers primarily in their ease of fabrication. Like traditional elastomers they offer benefits including reduction in noise emissions and improved wear resistance in metal components that are in contact with such parts in the railcar suspension system. However, viscoelastic materials, such as the railroad bearing thermoplastic elastomer suspension element (or elastomeric pad), are known to develop self-heating (hysteresis) under cyclic loading, which can lead to undesirable consequences. Quantifying the hysteresis heating of the pad during operation is therefore essential to predict its dynamic response and structural integrity, as well as, to predict and understand the heat transfer paths from bearings into the truck assembly and other contacting components. This study investigates the internal heat generation in the suspension pad and its impact on the complete bearing assembly dynamics and thermal profile. Specifically, this paper presents an experimentally validated finite element thermal model of the elastomeric pad and its internal heat generation. The steady-state and transient-state temperature profiles produced by hysteresis heating of the elastomer pad are developed through a series of experiments and finite element analysis. The hysteresis heating is induced by the internal heat generation, which is a function of the loss modulus, strain, and frequency. Based on previous experimental studies, estimations of internally generated heat were obtained. The calculations show that the internal heat generation is impacted by temperature and frequency. At higher frequencies, the internally generated heat is significantly greater compared to lower frequencies, and at higher temperatures, the internally generated heat is significantly less compared to lower temperatures. However, during service operation, exposure of the suspension pad to higher loading frequencies above 10 Hz is less likely to occur. Therefore, internal heat generation values that have a significant impact on the suspension pad steady-state temperature are less likely to be reached. The commercial software package ALGOR 20.3TM is used to conduct the thermal finite element analysis. Different internal heating scenarios are simulated with the purpose of obtaining the bearing suspension element temperature distribution during normal and abnormal conditions. The results presented in this paper can be used in the future to acquire temperature distribution maps of complete bearing assemblies in service conditions and enable a refined model for the evolution of bearing temperature during operation

Development of Methods for Determining Dry Deposition of Mercury Using an Ion-exchange membrane: Relative Rates of Mercury Dry Deposition at Sardis, Enid, and Grenada Lakes

This research focuses on studies developing methods to measure dry deposition of mercury (Hg) using an ion-exchange (IX) membrane to capture gaseous mercury species in the air. Mercury is a toxic heavy metal that is spread globally through the atmosphere. Atmospheric Hg deposits to terrestrial and aquatic ecosystems through wet and dry deposition. While routine methods have been developed to study wet deposition of Hg, measuring dry deposition of Hg is more problematic and often overlooked. In this study, we developed an inexpensive means to deploy a polyethersulfone cation exchange membrane in the field by dangling it within a polycarbonate bottle containing holes in the bottom to allow gas exchange. We tested several different analytical methods to measure the Hg on the membranes including atomic absorption spectrometry, atomic fluorescence spectrometry, and mass spectrometry. After demonstrating that the field method is capable of capturing and retaining airborne Hg on the membrane, we deployed the bottles containing the membranes at Sardis, Enid, and Grenada Lakes, located in north Mississippi. The purpose was to estimate the relative rates of dry deposition of Hg in order to explore differences in the levels of Hg found in fish from these lakes. We hypothesized that point sources near Grenada Lake, including a coal-fired power plant, may result in higher Hg deposition rates, which may be the reason for the higher Hg levels observed in fish from Grenada Lake compared to the other lakes. However, results show that Sardis Lake had the highest dry deposition rates followed by Enid and Grenada Lakes. Thus, the higher levels of Hg in fish from Grenada Lake remain unexplained

Regional Dynamic Viscoelastic Properties of Porcine Sclera

The biomechanical properties of the posterior sclera are thought to be important in glaucoma susceptibility. Assessment of the posterior sclera biomechanics is currently unavailable in vivo but methods are being developed to characterize the biomechanical properties of the anterior portion of the eye. The objective of this study was to characterize the regional dynamic viscoelastic properties of porcine sclera to examine possible correlation between anterior and posterior sclera. Scleral strips were excised from the temporal region of the anterior and posterior portions of 30 porcine eyes within 24 hours post-mortem. The scleral strips were tested using a Rheometrics Systems Analyzer II in a humidity chamber at approximately 25 °C. A cyclic strain was applied to the strips and the cyclic stress output was recorded. A ramp test was also conducted. The biomechanical properties of the anterior and posterior scleral showed significant differences with a complex modulus of 1.67±0.63 and 0.35±0.1 MPa (p0.25) or any biomechanical properties between the anterior and posterior sclera (p>0.82). These results provide insight to an interesting regional variance of the biomechanical properties of scleral tissue, which is not necessary proportional in the same eye. Future work will investigate scleral tissue microstructure to understand the structural basis of the mechanical difference from anterior to posterior eye.URS - College of EngineeringJun Liu, Ph.D, RO1EY020929No embargoAcademic Major: Biomedical Engineerin