PARAMETRIC STUDY OF REAXFF SIMULATION PARAMETERS FOR MOLECULAR DYNAMICS MODELING OF REACTIVE CARBON GASES

Abstract The development of innovative carbon-based materials can be greatly facilitated by molecular modeling techniques. Although the Reax Force Field (ReaxFF) can be used to simulate the chemical behavior of carbon-based systems, the simulation settings required for accurate predictions have not been fully explored. Using the ReaxFF, molecular dynamics (MD) simulations are used to simulate the chemical behavior of pure carbon and hydrocarbon reactive gases that are involved in the formation of carbon structures such as graphite, buckyballs, amorphous carbon, and carbon nanotubes. It is determined that the maximum simulation time step that can be used in MD simulations with the ReaxFF is dependent on the simulated temperature and selected parameter set, as are the predicted reaction rates. It is also determined that different carbon-based reactive gases react at different rates, and that the predicted equilibrium structures are generally the same for the different ReaxFF parameter sets, except in the case of the predicted formation of large graphitic structures with the Chenoweth parameter set under specific conditions

Seperation Of Fuel-Based Contaminents From Oxygen Carriers In Chemical Looping Combustion

This project involved the development of a technology for segregating fuel-based contaminants (char) from oxygen carrier material in the context of chemical looping combustion (CLC) application. In chemical looping, the well-mixed solids that flow from the fuel reactor consisting of char and oxygen carrier particles cannot be completely separated into their constituents before they enter the air reactor. The slip of carbon leads to char oxidation in the wrong reactor and poor carbon dioxide separation efficiency. An efficient method to separate char from oxygen carrier material is critical for the deployment of chemical looping technology. This segregation system consists of a novel combination of methodologies that together provide high separation efficiency under the extreme conditions of chemical looping systems. Experimental results obtained from this project have shown that separation of char from varying particle size distributions of oxygen carrier (ilmenite) are achievable under both ambient and elevated temperatures (300-400℃). Tests show that separation efficiency is directly impacted by the average particle size of the oxygen carrier relative to char. Results suggest that as oxygen carrier particles undergo attrition due to cycling in a chemical looping combustion system, a higher oxygen carrier recycle (split) is necessary in order to maintain high separation. The technology and test methods developed have demonstrated the ability to improve carbon capture rates within chemical looping combustions systems and will continue to undergo development with the goal of lowering greenhouse gas emissions from fossil fuel combustion

THE EFFECT OF IONOSPHERIC CONDUCTIVITY ON MAGNETOSPHERIC DYNAMICS

The connection between ionospheric conductivity and the dynamics of the magnetosphere was investigated, using several methods to change the ionospheric conductivity and then study the resultant changes to the magnetosphere. Computer simulations of the Earth\u27s geospace environment were utilized using OpenGGCM coupled with an ionosphere model CTIM and a ring current model RCM. Three methods were used to modify ionospheric conductivity. The incoming particle precipitation was modified by several orders of magnitude $\alpha=.01,.1,1,10$, the ionospheric conductivity was increased or decreased by factors $\beta=.25, .5, 1, 2,$ and $4$, and for the last method differing values of $F_{10.7}$, $70,110, 150, 200,$ and $250$ were used. Each of the methods is different because $F_{10.7}$ mostly affects the dayside, while precipitation mostly affects the nightside, then using the $\beta$ changes the conductivity over the whole ionosphere. This gives a good range for studying the effects of ionospheric conductivity on the magnetosphere. The magnetospheric dynamics studied are: the dayside magnetopause location, the reconnection rate of the Earth\u27s magnetosphere, X-line formation in the magnetotail, and substorm dynamics, both the frequency and magnitude of substorm occurrence. To understand the effect of particle precipitation on conductivity two events were simulated, a calm period on 4 May 2005 and a strong storm period on 17 March 2013. Scaling the precipitation energy flux by several orders of magnitude, conductivities in the auroral oval were influenced which, in turn, influence the cross polar cap potentials. With the change in conductance, magnetospheric convection is enhanced or reduced, and the location of the subsolar distance of the magnetopause can change by up to one $R_E$. The investigation of the reconnection rate for the varying precipitation simulations using the Hesse-Forbes-Bern method shows that particle precipitation affects the magnetic reconnection rate in these two events. The most notable differences, up to 40\%, occur on short time scales, that is, hours. A relation for longer time scales (tens of hours) between precipitation and reconnection for these two events is more difficult to ascertain. Differences in cross polar cap potential (CPCP) and reconnection rate (R) can be explained by viscous interactions and polar cap saturation. When precipitation was decreased, polar conductance was decreased, viscous interactions are stronger, and CPCP is higher than R. For high precipitation, high conductance cases the polar cap is in the saturation regime and CPCP is lower than R. Hemispheric asymmetries were found in the cross polar cap potential and in the calculated reconnection rate derived from the Northern and Southern Hemispheres. The majority of this research has already been published in the Journal of Geophysical Research: Space physics, Particle Precipitation Effects on Convection and the Magnetic Reconnection Rate in Earth\u27s Magnetosphere https://doi.org/10.1002/2017JA024030 For the whole ionospheric conductivity study, different values of $\beta=$, $.25, .5, 1, 2, 4$ were used to modify the ionospheric conductivity after it had been calculated by the ionosphere model. A moderate storm period, 16 May 2011 was simulated. Many of the same conclusions found in the precipitation study were found in this study as well, such as, CPCP decreasing as conductivity increases, the point at which the polar cap saturates decreases with increasing conductivity, and reconnection rates change on short time scales, but the overall average rate remains very similar. The incoming precipitation was used to identify auroral brightening that is linked with substorms. The criteria for auroral brightenings used in this study is where the maximum precipitation increased by at least $1 \ mW/m^2$ within 20 minutes. The criteria for substorms is that the maximum precipitation increases by 80\% within 20 minutes. Identifying all the auroral brightenings and substorms showed that as conductivity increased the maximum amount of precipitation decreased, and also the number and frequency of both the substorms and auroral brightenings decreased. The occurrence of extended X-lines in the magnetotail was analyzed, where if an earthward flow of greater than 50 km/s extended for greater than 10 $R_e$ in $Y_{GSE}$ was classified as an extended X-line. This is not to be confused with a bursty bulk flow or dipolarization front, which happen from reconnection but usually do not have a large extent in $Y_{GSE}$. Identifying extended X-lines in this manner showed a similar trend that as conductivity increased the number of extended X-lines decreased, and while there was not much of an indication if the size or location is affected much, the amount of time the simulation had extended X-lines present decreased. For the $F_{10.7}$ study, using values of $70, 110, 150, 200,$ and $250$, the ionospheric conductivity was influenced mostly on the dayside. A day during the spring equinox was simulated with ideal solar wind conditions as well as the 16 May 2011 storm period. The main results found is that $F_{10.7}$ does not affect the system as much as the precipitation study, or the whole ionosphere conductivity study, but there are still some indications that show the same conclusions obtained previously

Organisation des Produktmanagements : State-of-practice und Trends in verschiedenen Bereichen

Seit über siebzig Jahren ist das Produktmanagement (PM) in vielen Unternehmen eine feste Größe. In den letzten Jahren mehren sich jedoch Stimmen, die das PM in Frage stellen. Zum einen zweifeln einige Studien an der Marktnähe und Kundenorientierung des PM. Zum anderen werden neue Querschnittsfunktionen im Unternehmen geschaffen (z.B. Key Account Management, Vertriebscontrolling, Asset Management, Preis-Spezialisten), die sich mit dem PM überlappen. Deshalb untersucht die vorliegende Studie den State-of-Practice und die Trends in der Organisation des PM: Welche alternativen Lösungen zur organisatorischen Aufhängung des PM existieren? Wieviel Einfluss wird das PM zukünftig auf welche Entscheidungen in Marketing und Vertrieb haben? Wo bestehen im PM Reibungsverluste? Die Studie untersucht sowohl Konsumgüterhersteller als auch mehrere Industriegüterbranchen

A Low-Cost Attitude Determination and Control System and Hardware-in-the-Loop Testbed for CubeSats

The attitude determination and control system (ADCS) for a satellite is responsible for multiple key roles in a satellite’s mission, including detumbling the satellite after deployment, pointing payload sensors, and orienting antennas and solar panels for effective communication and power generation. Designing an effective ADCS is crucial to a mission’s success; however, current methods often rely on actuators and sensors that are bulky and expensive, such as reaction wheels and star trackers. While these systems can provide high accuracy, they often cannot be used on CubeSats due to volume, weight, and cost restrictions. This work builds upon PyCubed, a radiation-tolerant avionics platform for CubeSats that is programmable entirely in Python, by adding a low-cost, open-source attitude determination and control system that is scalable to smaller spacecraft like 1U CubeSats. This system relies on simple consumer-grade magnetometers, gyroscopes, and sun sensors to estimate the orientation of the satellite, along with a set of magnetic torque coils for actuation. By combining these low-cost sensors and actuators with sophisticated calibration, estimation, motion planning, and control software, we are able to achieve full three-axis attitude determination and control. The system is also completely solid-state, with no moving parts or need for consumable propellant, greatly reducing the chance of hardware failure. To further improve the development cycle and increase success rates for CubeSat missions, we have also developed an open-source hardware-in-the-loop simulator to enable rapid testing of ADCS algorithms and other flight software. The result is a robust, open-source development suite for CubeSats that is low cost, easy to program, and reliable

Dynamically-Induced Frustration as a Route to a Quantum Spin Ice State in Tb2Ti2O7 via Virtual Crystal Field Excitations and Quantum Many-Body Effects

The Tb$_2$Ti$_2$O$_7$ pyrochlore magnetic material is attracting much attention for its {\em spin liquid} state, failing to develop long range order down to 50 mK despite a Curie-Weiss temperature $\theta_{\rm CW} \sim -14$ K. In this paper we reinvestigate the theoretical description of this material by considering a quantum model of independent tetrahedra to describe its low temperature properties. The naturally-tuned proximity of this system near a N\'eel to spin ice phase boundary allows for a resurgence of quantum fluctuation effects that lead to an important renormalization of its effective low energy spin Hamiltonian. As a result, Tb$_2$Ti$_2$O$_7$ is argued to be a {\em quantum spin ice}. We put forward an experimental test of this proposal using neutron scattering on a single crystal.Comment: 5 pages, 3 figures. Version 2 has a modified introduction. Figure 2b of version 1 (experimental neutron scattering has been removed. A proposal for an experimental test is now included accompanied by a new Figure (Fig. 3

Critical review of the United Kingdoms "gold standard" survey of public attitudes to science

Since 2000, the UK government has funded surveys aimed at understanding the UK public’s attitudes toward science, scientists, and science policy. Known as the Public Attitudes to Science series, these surveys and their predecessors have long been used in UK science communication policy, practice, and scholarship as a source of authoritative knowledge about science-related attitudes and behaviors. Given their importance and the significant public funding investment they represent, detailed academic scrutiny of the studies is needed. In this essay, we critically review the most recently published Public Attitudes to Science survey (2014), assessing the robustness of its methods and claims. The review casts doubt on the quality of key elements of the Public Attitudes to Science 2014 survey data and analysis while highlighting the importance of robust quantitative social research methodology. Our analysis comparing the main sample and booster sample for young people demonstrates that quota sampling cannot be assumed equivalent to probability-based sampling techniques