Discrepancies between expected and observed rotation curves in spiral galaxies are commonly interpreted as evidence for the existence of dark matter. Dark matter can explain the observed flat ...rotation curves at the outer radii. However, some rotation curves of spiral galaxies exhibit rising features at large distances from the galactic centers that cannot be attributed to dark matter alone. Addition of magnetic field contribution to the rotation curves of spiral galaxies has been proposed in some literature to explain the rising features. In this work we investigated the rotation curves of three spiral galaxies, i.e. NGC 2841, NGC 6946, and M 31, whose profiles of azimuthal magnetic field are available in literature. In general, decomposition scenarios using four components (stellar disk, gas, bulge, and dark matter halo) with magnetic field fit better to the observational data.
Fragmentation and fission of giant molecular clouds occasionally results in a pair of gravitationally bound star clusters that orbit their mutual centre of mass for some time, under the influence of ...internal and external perturbations. We investigate the evolution of binary star clusters with different orbital configurations, with a particular focus on the Galactic tidal field. We carry out N-body simulations of evolving binary star clusters and compare our results with estimates from our semi-analytic model. The latter accounts for mass-loss due to stellar evolution and two-body relaxation, and for evolution due to external tides. Using the semi-analytic model, we predict the long-term evolution for a wide range of initial conditions. It accurately describes the global evolution of such systems, until the moment when a cluster merger is imminent. N-body simulations are used to test our semi-analytic model and also to study additional features of evolving binary clusters, such as the kinematics of stars, global cluster rotation, evaporation rates, and the cluster merger process. We find that the initial orientation of a binary star cluster with respect to the Galactic field, and also the initial orbital phase, is crucial for its fate. Depending on these properties, the binaries may experience orbital reversal, spiral-in, or vertical oscillation about the Galactic plane before they actually merge at t ... 100 Myr, and produce rotating star clusters with slightly higher evaporation rates. The merger process of a binary cluster induces an outburst that ejects ~10 per cent of the stellar members into the Galactic field. (ProQuest: ... denotes formulae/symbols omitted.)
Clusters of galaxies are the most massive structures in the Universe, confined together in gravitationally bound systems with typical mass in the range of 1013 M⊙−1015 M⊙. Clusters of galaxies may be ...considered as self-similar, meaning that the properties of low mass clusters can be scaled up from the properties of more massive clusters, and vice versa. Clusters of galaxies have been thought to have standard mass fraction of gas, independent of their redshifts or total masses, and therefore proposed to be used as "standard buckets".The purpose of this work is to check the validity of clusters of galaxies as standard buckets by studying larger sample than those analysed by Mantz et al. (2014). The data set employed here consists of Chandra observations of 47 relaxed clusters at redshift 0.069 ≤ z ≤ 1.063. The results of this study show that compared to the differential gas fraction (fgas,diff), the cumulative gas mass fractions (fgas,2500) of the total sample of clusters are less dependent to the total mass M2500 and redshift. Relation between gas mass fraction and total mass M2500 suggests that massive clusters are more reliable to be used as standard buckets.
Abstract
The perturbations to the Milky Way cause the disk to have bending or breathing wave, flare, and warp. Both spatial analyses from stellar and gas show the Milky Way warp can be approached ...with sinusoidal function to the Galactocentric longitude. In this research, we aim to find evidence of the transient Milky Way warp using kinematics data of the Red Giant Branch (RGB) stars from Gaia Data Release 2. We only use RGB stars with positive parallaxes and small parallax uncertainties where
ϖ
> 0 and
ϖ
/
σ
ϖ
> 5, respectively. Using the linear warp model, we find the Milky Way warp starts on
R
w
= 10.72 kpc, with the amplitude (
γ
w
) of 0.39 and the Line of Node lies on
ϕ
w
= −5.26°. Assumed the warp is a static long-lived feature on kinematics distribution, where all of the warp parameters are constant by the time, the observed vertical velocity (
V
z
) is less than the expected one. The maximum
V
z
is not exceeded to 12.5 km/s rather 20 km/s derived from the proposed model. It infers that the warp drive on the Milky Way is a transient feature. One of the possible reasons is the recent interaction with satellite galaxies in perturbing the outer disk of the Milky Way.
This study aimed to evaluate the prevalence and risk factors of infant dyschezia as well as pediatrician awareness regarding this disease in Indonesia.
This is a two-part cross-sectional study, which ...was divided into study A and B. Study A: Parents whose infants were under 9 months old and attended well-baby clinics were recruited at two randomly selected primary health centers. Parents also provided information on the infant's previous medical history, and socio-demographic and family details. The Rome IV criteria was translated and validated to be used for diagnosis of infant dyschezia. Study B: Randomly selected pediatricians were surveyed by using a questionnaire to evaluate their knowledge regarding infant dyschezia.
The prevalence of infant dyschezia based on the result of this study was 11.8%. Three risk factors had a significant relationship with infant dyschezia i.e., the number of children in the family (odds ratio OR, 5.619; 95% confidence interval CI, 2.194-14.390;
<0.001), complementary food diet (OR, 4.238; 95% CI, 1.902-9.443;
<0.001), and social-emotional disturbance (OR, 5.670; 95% CI, 2.550-12.609;
<0.001). The percentage of pediatricians correctly diagnosed infant dyschezia was 71.5%. Most pediatricians agreed that they did not perform any diagnostic testing (79.7%) and only provided education in cases of infant dyschezia (58.5%).
The prevalence of infant dyschezia identified in our study was higher than that in other neighboring Asian countries, with the highest prevalence observed in infants 7-9 months old. Being an only child, receiving complementary food diet, and sociao-emotional disturbances were significant risk factors of infant dyschezia.
This study aimed to look at the level of physics problem-solving ability achieved by students and identify the level of metacognition based on the ability to solve physics problems at each level. The ...research method used was a mixed method with a sequential explanatory strategy. The populations in this study were all eleventh-grade science students of Kebumen Islamic High School, Tanggamus District. The sampling technique used was a balanced sample with a participant selection model. The instruments used in this study were the physics tests, interviews, and documentation. The data analysis process included two stages of analysis, namely quantitative data analysis and qualitative data analysis. The results of this study indicated that 12.12% of students belong to the high problem-solving group, 66.67% of students belong to the moderate problem-solving group, and 21.21% of students belong to the low problem-solving group. The high problem-solving group had a high level of metacognition, namely Semi-reflective use with a percentage of 10% and Strategic use with a percentage of 10%. The moderate problem-solving group had Semi-strategic use level with a percentage of 40% and Aware use with a percentage of 20%. The low problem-solving group had the lowest metacognition level, namely Tacit use with a percentage of 20% of the total sample taken. so, the levels of metacognition ability of students in learning physics identified in this study were: tacit use, aware use, semi strategic use, strategic use, and semi-reflective use.
A universe containing a coupled scalar field would have different dynamical evolution compared to uncoupled cases. Significant differences are expected to emerge during matter dominated era, where ...scalar field density mimics how matter density evolves, by becoming subdominant. Analysis of the dynamics was investigated both analytically and numerically through phase plane method, and we obtained two attractor solutions which are compatible to a late time cosmic acceleration as the ending of matter dominated era. Ordinary scalar field triggers an acceleration with stable attractor solution which converges to ωϕ = ωeff ≈ −1. Whereas, phantom scalar field allows negative values for its own energy (ωeff ˂ −1 and Ωϕ ˂ 0); however this is not stable, therefore it will be caught by attractor solution which is stable to ωϕ = ωeff ≈ −1. In addition, we found cosmological parameters generated from both analytical and numerical calculations, i.e. ωϕ, Ωϕ and ωeff, by assuming a flat universe. The existence of a coupling constant Q between scalar field and matter induces different structure growth compared to uncoupled cases and standard cold dark matter (CDM) model. During matter dominated era, ordinary scalar field induces growth of structures so that it becomes faster than the standard model does, whereas phantom scalar field slows down the growth of structures. During scalar field dominated era (far in the future), we obtained that formed structures or density contrasts will decay in a similar way as in uncoupled cases, whereas following phantom scenario, the decay of formed structures occurs faster and more significant. This result is associated to background dynamics which shows that big rip will be the relevant fate of our universe.
Ultraluminous X-ray sources (ULXs) are known as extragalactic point-like X-ray sources with luminosities considerably in excess of the maximum luminosity of a 10 solar mass accreting black hole. ...X-ray spectra of ULXs have been investigated in many previous studies. However, sparse observations render it more difficult to convincingly distinguish between two competing scenarios, i.e. sub-critical accreting intermediate-mass black hole and super-critical accreting stellar remnant black hole. Here, we report our investigation of a sample of nearby ULXs, as well as their host galaxies, in order to get a more complete understanding of their nature. Multiwavelength analysis was applied to study these ULXs. From X-ray study, we found that most ULXs in our sample do exhibit spectral variability in which higher energy X-ray predominates the spectra as the source becomes brighter. We also compiled some properties of the host galaxies, as a proxy of ULX environment. We found that ULXs in our sample can neither be exclusively associated with a certain type of morphology, nor with high nuclear activity. We also found that 12 out of 19 ULXs reside in host galaxies with star formation rate of less than 1 solar mass per year.
The majority of students in the department of pre-service elementary school teacher cannot read the notation correctly. However, they have a strong motivation to learn music composition, such as ...angklung music composition. This paper aims to analyze the development of students who are members of the music community in studying the composition of angklung music by using the Synthesia application. The research method was carried out in the following stages: (1) making angklung musical composition in the type of MIDI (Musical Instrument Digital Interface) files; (2) input MIDI files for the Synthesia application; (3) setting up the Synthesia application; (4) learning Angklung using the Synthesia application; and (5) evaluating the learning process. Research subjects were students who were members of the music community on campus, so that their age and musical abilities were very heterogeneous. The research subjects were 15 people, as many as one angklung player group. The results showed that angklung learning for students who had the low notation reading ability, became easier by using a touch of technology. Students can read, visual-based notation correctly. It can be concluded; that technology can provide the convenience in the process of learning music composition, especially in angklung music composition.
The aim of this research is to detect misconceptions in the concept of physics at high school level by using astronomy questions as a testing instrument. Misconception is defined as a thought or an ...idea that is different from what has been agreed by experts who are reliable in the field, and it is believed to interfere with the acquisition of new understanding and integration of new knowledge or skills. While lack of concept or knowledge can be corrected with the next instruction and learning, students who have misconceptions have to "unlearn" their misconception before learning a correct one. Therefore, the ability to differentiate between these two things becomes crucial. CRI is one of the methods that can identify efficiently, between misconceptions and lack of knowledge that occur in the students. This research used quantitative- descriptive method with ex-post-facto research approach. An instrument used for the test is astronomy questions that require an understanding of physics concepts to solve the problem. By using astronomy questions, it is expected to raise a better understanding such that a concept can be viewed from various fields of science. Based on test results, misconceptions are found on several topics of physics. This test also revealed that student's ability to analyse a problem is still quite low.
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