Neutralizer optimization

The preliminary results of a test program to optimize a neutralizer design for 30 cm xenon ion thrusters are discussed. The impact of neutralizer geometry, neutralizer axial location, and local magnetic fields on neutralizer performance is discussed. The effect of neutralizer performance on overall thruster performance is quantified, for thruster operation in the 0.5-3.2 kW power range. Additionally, these data are compared to data published for other north-south stationkeeping (NSSK) and primary propulsion xenon ion thruster neutralizers

Dimensional Reduction, Seiberg--Witten Map and Supersymmetry

It is argued that dimensional reduction of Seiberg-Witten map for a gauge field induces Seiberg-Witten maps for the other noncommutative fields of a gauge invariant theory. We demonstrate this observation by dimensionally reducing the noncommutative N=1 SYM theory in 6 dimensions to obtain noncommutative N=2 SYM in 4 dimensions. We explicitly derive Seiberg-Witten maps of the component fields in 6 and 4 dimensions. Moreover, we give a general method to define the deformed supersymmetry transformations that leaves the actions invariant after performing the Seiberg-Witten maps.Comment: 14 pages. One Ref. added. To appear in PR

Navigating Workload Compatibility Between a Recommender System and a NoSQL Database: An Interactive Tutorial

In this tutorial, the issue of compatibility between a big data storage technology and an analytic workload is explored using a fictitious streaming company as an example. The tutorial offers an interactive approach to help students understand the importance of considering workload compatibility when adopting new technologies. We provide instructors with two Jupyter Notebooks that analyze the compatibility, a detailed instructor guide on how to execute these notebooks, lessons learned, and appendices containing solutions and explanations. This tutorial provides a valuable resource for instructors teaching courses in database systems, big data, and analytic concepts, helping students develop practical skills to navigate the complexities of big data technologies effectively

Purchase Behaviors During Emergencies: Exploratory Analyses and Predictive Models

In this study, we distinguish between traditional emergency events (i.e., those that occur frequently) and novel emergency events (i.e., those that occur rarely in one’s lifetime). We examine consumers’ shopping behaviors during both types of emergency events. Using data from a U.S. supermarket chain, we answer three research questions. First, we conduct multiple cluster analyses and identify three distinct shopping behaviors during emergency events, namely strategic, routine, and stocking. Second, we examine how consumers change their shopping behaviors toward novel emergency events and find that majority of consumers continue to engage in routine shopping behaviors. Third, we examine how to predict shopping behaviors before emergency events and show that all three types of shopping behaviors can be predicted with reasonable levels of accuracy based on consumers’ spending before emergency events

What is on Tap? The Role of Spin in Compact Objects and Relativistic Jets

We examine the role of spin in launching jets from compact objects across the mass scale. Our work includes a total of 37 Seyferts, 11 stellar-mass black holes, and 13 neutron stars. We find that when the Seyfert reflection lines are modeled with Gaussian line features (a crude proxy for inner disk radius and therefore spin), only a slight inverse correlation is found between the Doppler-corrected radio luminosity at 5 GHz (a proxy for jet power) and line width. When the Seyfert reflection features are fit with relativistically-blurred disk reflection models that measure spin, there is a tentative positive correlation between the Doppler-corrected radio luminosity and the spin measurement. Further, when we include stellar-mass black holes in the sample, to examine the effects across the mass scale, we find a slightly stronger correlation with radio luminosity per unit mass and spin, at a marginal significance (2.3 sigma confidence level). Finally, when we include neutron stars, in order to probe lower spin values, we find a positive correlation (3.3 sigma confidence level) between radio luminosity per unit mass and spin. Although tentative, these results suggest that spin may have a role in determining the jet luminosity. In addition, we find a slightly more significant correlation (4.4 sigma confidence level) between radio luminosity per Bolometric luminosity and spin, using our entire sample of black holes and neutrons stars. Again, although tentative, these relations point to the possibility that the mass accretion rate, i.e. Bolometric luminosity, is also important in determining the jet luminosity, in addition to spin. Our analysis suggests that mass accretion rate and disk or coronal magnetic field strength may be the "throttle" in these compact systems, to which the Eddington limit and spin may set the maximum jet luminosity that can be achieved.Comment: 14 pages, 13 Figures, ApJ Accepte

Boussinesq Modelling of Waves and Currents in the Presence of Submerged Detached/Discontinuous Breakwaters

The effect of beach configurations with the main focus on the detached submerged breakwater on shoreline currents is investigated numerically. The Boussinesq equations are used to model the beach with a constant slope, continuous submerged breakwater, and discontinuous/detached submerged breakwater. Our numerical simulation results show that the transient rip currents are generated near the shoreline at the beach with constant slope while the continuous submerged breakwater structure creates a calm beach area along the shoreline. The presence of the gap in submerged breakwater changes the currents along the shoreline by generating rip currents with two pairs of vortices. One pair of vorticities, located around the gap, damage the breakwater by transmitting sediments along the breakwater foundation and eroding its surface. The second pair, created near the shoreline, erodes the shoreline due to sediment transportation and leads to a dangerous and unsafe situation for swimmers. The rip current creates five main critical areas with the maximum velocity towards the shoreline and offshore. The first set of three areas (numbered 1, 2, 3) has an approximately average velocity of 1-1.25 m/s towards the shoreline. One of these areas (numbered 2) is located close to the shoreline and the other two (numbered 1 and 3) are found to occur near the edge of the detached part of the breakwater. The second set of the two areas (numbered by 4 and 5) has the average velocity that is higher than 2.1 m/s towards the offshore and is located at the beginning part of the rip neck. An approximately linear relationship between the returning velocity and the gap length is observed. As the gap length decreases the location of the areas (numbered 4 and 5) gets closer to the center of the gap. Our simulations indicate that the return velocity towards the offshore increases at the gap center while the gap length decreases. Furthermore, the velocity profiles have a sharp jump for gap length that is approximately smaller than 80 m. Also, the return velocity at the gap center is related to the height of the breakwater. The breakwater that is higher (the breakwater height d = 4.2 m) damps wave energy more than shorter breakwater and the return velocity decreases for this structure. For smaller heights (d = 3.7 and 3.2) damping is nearly the same and the returning flow varies depending on the available space through the gap. Specifically, the return velocity for d = 3.7 is higher than that for d = 3.2. The numerical results presented herein suggest that aggressive rip currents are generated in the case of detached submerged breakwater beach configurations

An experimental investigation of chatter effects on tool life

Tool wear is one of the most important considerations in machining operations as it affects surface quality and integrity, productivity and cost. The most commonly used model for tool life analysis is the one proposed by F.W. Taylor about a century ago. Although the extended form of this equation includes the effects of important cutting conditions on tool wear, tool life studies are mostly performed under stable cutting conditions where the effect of chatter vibrations are not considered. This paper presents an empirical attempt to understand tool life under vibratory cutting conditions. Tool wear data are collected in turning and milling on different work materials under stable and chatter conditions. The effects of cutting conditions as well as severity of chatter on tool life are analyzed. The results indicate significant reduction in tool life due to chatter as expected. They also show that the severity of chatter, and thus the vibration amplitude, strongly reduces the life of cutting tools. These results can be useful in evaluating the real cost of chatter by including the reduced tool life. They can also be useful in justifying the cost of chatter suppression and more rigid machining systems

Study of multi black hole and ring singularity apparent horizons

We study critical black hole separations for the formation of a common apparent horizon in systems of $N$ - black holes in a time symmetric configuration. We study in detail the aligned equal mass cases for $N=2,3,4,5$, and relate them to the unequal mass binary black hole case. We then study the apparent horizon of the time symmetric initial geometry of a ring singularity of different radii. The apparent horizon is used as indicative of the location of the event horizon in an effort to predict a critical ring radius that would generate an event horizon of toroidal topology. We found that a good estimate for this ring critical radius is $20/(3\pi) M$. We briefly discuss the connection of this two cases through a discrete black hole 'necklace' configuration.Comment: 31 pages, 21 figure