Bitcoin and Ethereum: Empirical Evidence on Node Distribution

With the explosive growth in cryptocurrencies over the last couple of years, the cost of mining these technologies (the process through which users devote CPU power to operate the underlying blockchains) have similarly exploded. This paper examines one overarching question regarding this issue – what factor or factors explain the geographic distribution of cryptocurrency nodes (mining operations) across the world? In exploring this question, this research considers electricity price, internet access, Tor network relays, and others. Using node distribution data for Bitcoin and Ethereum – the two largest cryptocurrencies – this paper analyzes cross-sectional and panel data regression models, and establishes that electricity price has not played a significant role in this distribution up to this point, and concludes that the historical association between Tor relays and Bitcoin use has had a much greater impact. Lastly, this paper discusses the broader implications of its findings, and the potential areas of research for further understanding of this field

AIAA Design, Build, Fly: Aerodynamics

As part of the Santa Clara University Senior Design Project, the AIAA Design, Build, Fly: Aerodynamics team was responsible for designing and testing the wings, tail, and control surfaces of an aircraft designed to participate in future AIAA Design, Build, Fly competitions. Named Evergreen in honor of professor John J. Montgomery, the unmanned aerial vehicle was designed and constructed in collaboration with the AIAA Design, Build, Fly: Structures and Controls senior design team. Aiming to construct a competitive aircraft for the competition, the team decided that a target weight of approximately 3.5 kg and a cruise speed of 25 m/s would be the starting points of the design. For the general wing configuration, three options were considered: monoplane (low-wing), cantilever (high-wing), and biplane. The cantilever configuration presented the desired wing characteristics for this aircraft, such as higher lift, stability, and ease of manufacturing. To minimize wing loading and take-off speeds, a wingspan of 1.50 m was selected considering that the maximum dimension length permitted by the competition is 1.57 m (62 in). After conducting a selection study between several high-lift airfoils, the NACA 4416 airfoil would be the most suitable, with an optimal chord length of 0.3028 m due to the previously decided weight and velocity. For the wing control surfaces, a flaperon configuration was chosen instead of separate flap and aileron structures. Through the use of flaperons, the weight and complexity of the wing is reduced while maintaining the necessary functionality from the surfaces. To avoid unpredictable behavior due to vortices created at the inward tips of the flaperons, a maximum size of 42 cm was determined, which proved sufficient at providing relatively low take-off speeds (\u3c 15 m/s). In collaboration with the Structures and Controls team, the fuselage size was used to determine the optimal dimensions of the tail, minimizing drag and guaranteeing aircraft stability in all flight modes. For the stability study, XFLR5TM was utilized as it is a powerful tool that can accurately determine the stability of the aircraft in all eight relevant flight modes given the dimension of the wing, tail assembly, and the position of the center of gravity. For complete two and three-dimensional CFD analysis, SOLIDWORKSTM Flow Simulation and ANSYSTM Fluent were exploited in parallel between the many design iterations of the Evergreen, ensuring that the theoretical design produced the desired characteristics under simulated flight conditions. Through Flow Simulation, the sizing of the aerodynamic shape of the aircraft — wing and tail — proved sufficient to sustain the anticipated weight of the aircraft, and a flap deflection study provided security on the effectiveness of the flaps for lower takeoff speeds. Additionally, the CFD analysis was useful to estimate the forces and torques experiences by the control surfaces, which was in turn used by the Structures and Controls team to select the appropriate servo motors for each control surface. Once the design was deemed aerodynamically capable, the Evergreen was constructed as a joint effort of both teams. Containing minute differences in comparison to the CAD model of the aircraft, the Evergreen performed successfully in eight separate flights, satisfying the take-off distance, control, range, and payload capacity required by the competition. With the data provided in this project, the AIAA Design, Build, Fly: Aerodynamics team is confident that future generations of students can improve and adapt the Evergreen to compete for Santa Clara University

Turbulent Chemical Diffusion in Convectively Bounded Carbon Flames

It has been proposed that mixing induced by convective overshoot can disrupt the inward propagation of carbon deflagrations in super-asymptotic giant branch stars. To test this theory, we study an idealized model of convectively bounded carbon flames with 3D hydrodynamic simulations of the Boussinesq equations using the pseudospectral code Dedalus. Because the flame propagation timescale is much longer than the convection timescale, we approximate the flame as fixed in space, and only consider its effects on the buoyancy of the fluid. By evolving a passive scalar field, we derive a {\it turbulent} chemical diffusivity produced by the convection as a function of height, $D_{\rm t}(z)$. Convection can stall a flame if the chemical mixing timescale, set by the turbulent chemical diffusivity, $D_{\rm t}$, is shorter than the flame propagation timescale, set by the thermal diffusivity, $\kappa$, i.e., when $D_{\rm t}>\kappa$. However, we find $D_{\rm t}<\kappa$ for most of the flame because convective plumes are not dense enough to penetrate into the flame. Extrapolating to realistic stellar conditions, this implies that convective mixing cannot stall a carbon flame and that "hybrid carbon-oxygen-neon" white dwarfs are not a typical product of stellar evolution.Comment: Accepted to Ap