Speeding up the GENGA N-body integrator on consumer-grade graphics cards

Context. Graphics processing unit (GPU) computing has become popular due to the enormous calculation potential that can be harvested from a single card. The N-body integrator Gravitational ENcounters with GPU Acceleration (GENGA) is built to harvest the computing power from such cards, but it suffers a severe performance penalty on consumer-grade Nvidia GPUs due to their artificially truncated double precision performance. Aims. We aim to speed up GENGA on consumer-grade cards by harvesting their high single-precision performance. Methods. We modified GENGA to have the option to compute the mutual long-distance forces between bodies in single precision and tested this with five experiments. First, we ran a high number of simulations with similar initial conditions of on average 6600 fully self-gravitating planetesimals in both single and double precision to establish whether the outcomes were statistically different. These simulations were run on Tesla K20 cards. We supplemented this test with simulations that (i) began with a mixture of planetesimals and planetary embryos, (ii) planetesimal-driven giant planet migration, and (iii) terrestrial planet formation with a dissipating gas disc. All of these simulations served to determine the accuracy of energy and angular momentum conservation under various scenarios with single and double precision forces. Second, we ran the same simulation beginning with 40 000 self-gravitating planetesimals using both single and double precision forces on a variety of consumer-grade and Tesla GPUs to measure the performance boost of computing the long-range forces in single precision. Results. We find that there are no statistical differences when simulations are run with the gravitational forces in single or double precision that can be attributed to the force prescription rather than stochastic effects. The accumulations in uncertainty in energy are almost identical when running with single or double precision long-range forces. However, the uncertainty in the angular momentum using single rather than double precision long-range forces is about two orders of magnitude greater, but still very low. Running the simulations in single precision on consumer-grade cards decreases running time by a factor of three and becomes within a factor of three of a Tesla A100 GPU. Additional tuning speeds up the simulation by a factor of two across all types of cards. Conclusions. The option to compute the long-range forces in single precision in GENGA when using consumer-grade GPUs dramatically improves performance at a little penalty to accuracy. There is an additional environmental benefit because it reduces energy usage

Forming rocky exoplanets around K-dwarf stars

How multiple close-in super-Earths form around stars with masses lower than that of the Sun is still an open issue. Several recent modeling studies have focused on planet formation around M-dwarf stars, but so far no studies have focused specifically on K dwarfs, which are of particular interest in the search for extraterrestrial life. We aim to reproduce the currently known population of close-in super-Earths observed around K-dwarf stars and their system characteristics. We performed 48 high-resolution N-body simulations of planet formation via planetesimal accretion using the existing GENGA software running on GPUs. In the simulations we varied the initial disk mass and the solid and gas surface density profiles. Each simulation began with 12000 bodies with radii of between 200 and 2000 km around two different stars, with masses of 0.6 and 0.8 $M_{\odot}$. Most simulations ran for 20 Myr, with several simulations extended to 40 or 100 Myr. The mass distributions for the planets with masses between 2 and 12 $M_\oplus$ show a strong preference for planets with masses $M_p<6$ $M_\oplus$ and a lesser preference for planets with larger masses, whereas the mass distribution for the observed sample increases almost linearly. However, we managed to reproduce the main characteristics and architectures of the known planetary systems and produce mostly long-term angular-momentum-deficit-stable, nonresonant systems, but we require an initial disk mass of 15 $M_\oplus$ or higher and a gas surface density value at 1 AU of 1500 g cm$^{-2}$ or higher. Our simulations also produce many low-mass planets with $M<2$ $M_\oplus$, which are not yet found in the observed population, probably due to the observational biases. The final systems contain only a small number of planets, which could possibly accrete substantial amounts of gas, and these formed after the gas had mostly dissipated.Comment: 27 pages, 29 figures, to be published in Astronomy & Astrophysic

Cinema in the Age of AI

Filmmaking is an inherently technology-driven cultural art form. However, with the use of AI technology, creating an entire film's content using algorithms is increasingly becoming a possibility. This has led to concerns about how algorithmically-generated media might impact contemporary visual culture and our gaining of knowledge. In my research, I compare a well-known art film, Meshes of the Afternoon (1943), and a fully AI-scripted film, Sunspring (2016), to establish their respective implications on how we gain knowledge. By using texts from film studies, visual culture, and computational aesthetics, I determined the differences in AI versus human-made films. My findings demonstrate how the algorithmic technology provides a generalization of pre-existing data rather than of original processing of the real-world, as possible in human-made films. This results in a cyclical stage of knowledge in AI made media and creates the need to re-evaluate our increasing reliance on technology in artistic practices

Guiding of Tectonic Plate Motions by Transform Faults and Mid-Ocean Ridges

Transform faults are strike-slip faults that accommodate lateral offsets between spreading segments of mid-ocean ridges. Because plates cannot move perpendicular to them, transform faults may exert a control on plate motions that has not been considered earlier. To improve some discrepancies between the predicted and observed plate motions, we introduce a force that resists plate motions parallel to mid-oceanic ridges (an alternative to a force perpendicular to the transform faults) into a larger-scale force balance that has previously been used to predict plate movements. Using three different misfit functions: misfit in direction, misfit in amplitude, and misfit in both direction and amplitude together, we constrain the magnitude of the new force, and compare its values to that of the major plate-driving forces. Our estimates of the ridge-parallel resistance expressed as a stress at plate boundaries are in a range between 16.5 and 44.0~MPa (assuming an average lithospheric thickness of 10~km at transform faults). The model previously used to predict plate motions is generally most improved when we use a value at the lower end of this range, but the improvement is typically minor. Our estimates of the actual force are between 0.8 and \num{2.1e11}~N/m, which is two orders of magnitude smaller than the expected value of the slab pull force, and one order of magnitude smaller than an estimate for ridge push. In general, even though the contribution of the ridge-parallel resistance to the force balance is relatively small, it slightly improves the predictions of the plate motions

Pride is Dead, Long Live Pride: A Study of the Commodification of Identity Politics Through an Analysis of Matthew Warchus’ Pride (2014)

The transformation of pride from being a quality of economically disadvantaged groups who sought acceptable living standards to individuals engaging with a commodified ideal that rests upon celebrating uniqueness has created another item to be negotiated in the world marketplace, separating the haves from the have nots. While certain forms of marginalization benefit the middle-classes who strive for recognition in an increasingly anonymous world, such diverse and beautiful colours do little to clothe and feed the multitudes that still remain below poverty levels worldwide. Matthew Warchus’s Pride (2014) tells the story of the miners and the LGBTQI+ community supporting each other politically during Margaret Thatcher’s government, highlighting what was perhaps the last period in which such a coalition between two now distinct political groups was possible. The subsequent disintegration of class politics as the central focus of the left, replaced by a new emphasis on identity politics, created an atmosphere where some previously marginalized groups become integrated into the mainstream culture. Hence, the neoliberal capitalist system dismantled communal action through division that privileged distinct non-class-based identities as new commodities for exchange – eliminating the possibility of unity between those groups marginalized on the basis of race, gender, sexual orientation, etc. and those structurally subordinated due to class. Warchus' Pride provides one alternative that may have since then been lost. Still, if the political left is to regain its ability to prioritize equality, it must relinquish its bonds to the commodification that has begun to pervade its socio-political agenda

Speeding up the GENGA N-body integrator on consumer-grade graphics cards

Context. Graphics processing unit (GPU) computing has become popular due to the enormous calculation potential that can be harvested from a single card. The N-body integrator Gravitational ENcounters with GPU Acceleration (GENGA) is built to harvest the computing power from such cards, but it suffers a severe performance penalty on consumer-grade Nvidia GPUs due to their artificially truncated double precision performance. Aims. We aim to speed up GENGA on consumer-grade cards by harvesting their high single-precision performance. Methods. We modified GENGA to have the option to compute the mutual long-distance forces between bodies in single precision and tested this with five experiments. First, we ran a high number of simulations with similar initial conditions of on average 6600 fully self-gravitating planetesimals in both single and double precision to establish whether the outcomes were statistically different. These simulations were run on Tesla K20 cards. We supplemented this test with simulations that (i) began with a mixture of planetesimals and planetary embryos, (ii) planetesimal-driven giant planet migration, and (iii) terrestrial planet formation with a dissipating gas disc. All of these simulations served to determine the accuracy of energy and angular momentum conservation under various scenarios with single and double precision forces. Second, we ran the same simulation beginning with 40 000 self-gravitating planetesimals using both single and double precision forces on a variety of consumer-grade and Tesla GPUs to measure the performance boost of computing the long-range forces in single precision. Results. We find that there are no statistical differences when simulations are run with the gravitational forces in single or double precision that can be attributed to the force prescription rather than stochastic effects. The accumulations in uncertainty in energy are almost identical when running with single or double precision long-range forces. However, the uncertainty in the angular momentum using single rather than double precision long-range forces is about two orders of magnitude greater, but still very low. Running the simulations in single precision on consumer-grade cards decreases running time by a factor of three and becomes within a factor of three of a Tesla A100 GPU. Additional tuning speeds up the simulation by a factor of two across all types of cards. Conclusions. The option to compute the long-range forces in single precision in GENGA when using consumer-grade GPUs dramatically improves performance at a little penalty to accuracy. There is an additional environmental benefit because it reduces energy usage.ISSN:0004-6361ISSN:1432-074

Validity of Quinpirole Sensitization Rat Model of OCD: Linking Evidence from Animal and Clinical Studies

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder with 1-3% prevalence. OCD is characterized by recurrent thoughts (obsessions) and repetitive behaviors (compulsions). The pathophysiology of OCD remains unclear, stressing the importance of pre-clinical studies. The aim of this article is to critically review a proposed animal model of OCD that is characterized by the induction of compulsive checking and behavioral sensitization to the D2/D3 dopamine agonist quinpirole.. Changes in this model have been reported at the level of brain structures, neurotransmitter systems and other neurophysiological aspects. In this review, we consider these alterations in relation to the clinical manifestations in OCD, with the aim to discuss and evaluate axes of validity of this model. Our analysis shows that some axes of validity of quinpirole sensitization model (QSM) are strongly supported by clinical findings, such as behavioral phenomenology or roles of brain structures. Evidence on predictive validity is contradictory and ambiguous. It is concluded that this model is useful in the context of searching for the underlying pathophysiological basis of the disorder because of the relatively strong biological similarities with OCD