General relativistic magnetohydrodynamical simulations of the jet in M87

(abridged) The connection between black hole, accretion disk, and radio jet can be best constrained by fitting models to observations of nearby low luminosity galactic nuclei, in particular the well studied sources Sgr~A* and M87. There has been considerable progress in modeling the central engine of active galactic nuclei by an accreting supermassive black hole coupled to a relativistic plasma jet. However, can a single model be applied to a range of black hole masses and accretion rates? Here we want to compare the latest three-dimensional numerical model, originally developed for Sgr A* in the center of the Milky Way, to radio observations of the much more powerful and more massive black hole in M87. We postprocess three-dimensional GRMHD models of a jet-producing radiatively inefficient accretion flow around a spinning black hole using relativistic radiative transfer and ray-tracing to produce model spectra and images. As a key new ingredient to these models, we allow the proton-electron coupling in these simulations depend on the magnetic properties of the plasma. We find that the radio emission in M87 is well described by a combination of a two-temperature accretion flow and a hot single-temperature jet. The model fits the basic observed characteristics of the M87 radio core. The best fit model has a mass-accretion rate of Mdot approx 9x10^{-3} MSUN/YR and a total jet power of P_j \sim 10^{43} erg/s. Emission at 1.3mm is produced by the counter jet close to the event horizon. Its characteristic crescent shape surrounding the black hole shadow could be resolved by future millimeter-wave VLBI experiments. The model was successfully derived from one for the supermassive black hole in center of the Milky Way by appropriately scaling mass and accretion rate. This suggests the possibility that this model could also apply to a larger range of low-luminosity black holes.Comment: 15 pages, 14 figures, accepted to Astronomy and Astrophysics, after language proofs, with correct titl

Field-testing items using artificial intelligence: Natural language processing with transformers

Five thousand variations of the RoBERTa model, an artificially intelligent "transformer" that can understand text language, completed an English literacy exam with 29 multiple-choice questions. Data were used to calculate the psychometric properties of the items, which showed some degree of agreement to those obtained from human examinee data

Robust Latent Ability Estimation Based on Item Response Information and Model Fit

Aberrant testing behaviors may result in inaccurate person trait estimation. To counter its effects, a new robust ability estimation procedure called downweighting of aberrant responses estimation (DARE) is developed. This procedure downweights both uninformative items and model-misfitting response patterns. The purpose of this study is to present DARE and to evaluate its performance against other robust methods, including biweight (Mislevy & Bock, 1982) and biweight-MAP (BMAP; Maeda & Zhang, 2017b). The traditional maximum likelihood (MLE) and maximum a-posteriori (MAP) methods are also included as baseline methods. A Monte Carlo simulation is conducted with the design variables being test length, type of aberrant behaviors, percentage of aberrant examinees, and percentage of aberrant items. Person-fit analyses using l_z^* (Snijders, 2001) and H^T (Sijtsma, 1986) are incorporated as a realistic initial step to determine the aberrant examinees that might benefit from robust estimation methods. Results showed that DARE effectively decreased the root-mean-squared-error (RMSE) and bias of the estimates compared to MAP among examinees detected using the l_z^* at the .01 α cutoff. DARE was the most accurate method in many conditions involving aberrant behavior when the test length was 40 or 60 items. At 20 items, all robust methods were ineffective. DARE performs well when 1) a high-achieving examinee show a mild spuriously low scoring behavior, or 2) a low-achieving examinee show a mild spuriously high scoring behavior. When used appropriately, DARE is superior to all pre-existing methods in limiting the negative consequences of aberrant behavior

Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*

Radiatively inefficient accretion flows (RIAFs) are believed to power supermassive black holes (SMBH) in the underluminous cores of galaxies. Such black holes are typically accompanied by flat-spectrum radio cores indicating the presence of moderately relativistic jets. One of the best constrained RIAFs is associated with the SMBH in the Galactic center, Sgr A*. Since the plasma in RIAFs is only weakly collisional, the dynamics and the radiative properties of these systems are very uncertain. Here we want to study the impact of varying electron temperature on the appearance of accretion flows and jets. Using 3-D GRMHD accretion flow simulations, we use ray tracing methods to predict spectra and radio images of RIAFs allowing for different electron heating mechanisms in the in- and outflowing parts of the simulations. We find that small changes in the electron temperature can result in dramatic differences in the relative dominance of jets and accretion flows. Application to Sgr A* shows that radio spectrum and size of this source can be well reproduced with a model where electrons are more efficiently heated in the jet. The X-ray emission is sensitive to the electron heating mechanism in the jets and disk and therefore X-ray observations put strong constraints on electron temperatures and geometry of the accretion flow and jet. For Sgr A*, the jet model also predicts a significant frequency-dependent core shift which could place independent constraints on the model once measured accurately. We conclude that more sophisticated models for electron distribution functions are crucial for constraining GRMHD simulations with actual observations. For Sgr A*, the radio appearance may well be dominated by the outflowing plasma. Nonetheless, at the highest radio frequencies, the shadow of the event horizon should still be detectable with future Very Long Baseline Interferometric observations.Comment: A&A accepted, 11 figures, 1 tabl

The Effects of a Lifetime Physical Activity and Fitness Course on College Students’ Health Behaviors

International Journal of Exercise Science 9(2): 136-148, 2016. The purpose of this study was to examine motivational constructs and the effect of physical activity engagement on health behaviors in college students who were required to take a 15-week lifetime physical fitness (LPF) course for graduation. A total of fifty-eight first and second year college students aged between 17 and 23 years (M=18.72; SD=1.09). Paper and pencil questionnaires were anonymously administered at the beginning and at the end of the 15-week long spring 2012 semester. Analysis of the differences between the beginning and the end of the semester was completed. Physical activity behaviors and Behavioral Regulations variables did not change across time (p \u3e .05). Appearance (d = -0.34, p = .013) and fitness (d = -0.37, p = .006) reasons for participating in physical activity and all Theory of Planned Behavior variables decreased over time (d = -0.32 to -0.41, p \u3c .05). Changes in attitude toward physical activity negatively predicted changes in alcohol consumption (r = -.261 to -.357). This study sustains the already existing literature that supports the positive impact of LPF courses offered to college students

Assistive Systems for the Visually Impaired Based on Image Processing

In this chapter, we proposed three assistive systems for visually impaired individuals based on image processing: Kinect cane system, Kinect goggle system, and light checking system. The Kinect cane system can detect obstacles of various sizes and also recognize objects such as seats. A visually impaired user is notified of the results of detection and recognition by means of vibration feedback. The Kinect goggle system is another type of wearable system, and can make user’s hands free. The light checking system is implemented as an application for a smartphone, and can tell a visually impaired user the ON/OFF states of room lights and elevator button lights. The experimental results demonstrate that the proposed systems are effective in helping visually impaired individuals in everyday environments

Self-determined Engagement in Physical Activity and Sedentary Behaviors of US College Students

International Journal of Exercise Science 7(1) : 87-97, 2014. Although the importance of promoting physical activity is well established, researchers have recently considered “sedentary behaviors” as another key risk factor for chronic disease.However, little is known about the motivational processes regulating sedentary behavior on a daily basis. A substantial amount of research has been based on the self-determination theory to examine the motivational processes regulating physical activity behaviors. However, only limited attention has been paid to sedentary behaviors from this theoretical perspective. This study aims to identify and understand motivational aspects related to sedentary behavior from a self-determination perspective. A convenience sample of undergraduate students (N=875) enrolled in a university required Lifetime Physical Activity and Fitness class completed an online survey which inquired about physical activity and sedentary behaviors as well as about motivational variables related to these behaviors. Physical activity variables were inversely and only slightly related to sedentary behavior (ρ = -.084 to -.146, p \u3c .05). Psychological needs and behavioral regulations together explained 14.3% of the variance in moderate-to-vigorous physical-activity (p \u3c .001), but only 2.8% of the variance in sedentary behavior (p = .002). These findings suggest physical activity and sedentary behaviors are explained by unique motivational factors