arXiv subjects

Vahid Amiri

Publications and source records attributed to Vahid Amiri.

6 recordsLinked to original sources

arXiv2026

Primordial Binary Stars, Mass segregation and Fractality Effects on the Early Evolution of Young Open Clusters

We want to understand how the combined effect of initial substructure, primordial mass segregation, and primordial binaries affects the dynamical evolution of the cluster, and which one of these features is the most important to agree with observations. Methods. We use Nbody6++GPU to simulate the dynamics of star clusters with initial substructure, primordial mass segregation, and primordial binaries, and we also study the relative importance of the processes. Initial models were generated by a modified version of McLuster, and we compared our results with observational data from Pang et al. 2022 database of open clusters. Our results show that primordial mass segregation and binaries do not change the result already obtained in previous works, as the time scale on which initial substructure disappears is of the order of few Myrs. However, we also find that in the presence of initial substructure, primordial mass segregation does not lead to an early expansion of the cluster. The processes in the core, discussed in previous works, lead to a loss of low mass stars and early expansion, are postponed in the presence of initial substructure. Finally, we find from comparison with observed clusters that primordial mass segregation is not a fundamental process to reproduce observational data.

astro-ph.GA↗

arXiv2025

DRAGON-III simulation: modelling million-body globular and nuclear star clusters

As a continuation of DRAGON-II, we present the DRAGON-III project, which focuses on the simulations of million-body globular clusters and nuclear clusters over 10 Gyr. We report on its preliminary results on globular clusters. The first 100 Myr of the simulations have produced 41 pulsars, 191 X-ray binaries, 17 gravitational wave sources, and one black hole-black hole merger due to the loss of orbital energy in the form of gravitational wave emission. The inclusion of initial soft binaries brings surprisingly interesting results, including one IMBH in a binary black hole, and compact object binaries resembling the Gaia-BH1 and the wide black hole-giant binary reported in Wang et al. (2024, Nat. Astro.).

astro-ph.GA↗

arXiv2025

Sentiment Analysis in Twitter Social Network Centered on Cryptocurrencies Using Machine Learning

Cryptocurrency is a digital currency that uses blockchain technology with secure encryption. Due to the decentralization of these currencies, traditional monetary systems and the capital market of each they, can influence a society. Therefore, due to the importance of the issue, the need to understand public opinion and analyze people's opinions in this regard increases. To understand the opinions and views of people about different topics, you can take help from social networks because they are a rich source of opinions. The Twitter social network is one of the main platforms where users discuss various topics, therefore, in the shortest time and with the lowest cost, the opinion of the community can be measured on this social network. Twitter Sentiment Analysis (TSA) is a field that analyzes the sentiment expressed in tweets. Considering that most of TSA's research efforts on cryptocurrencies are focused on English language, the purpose of this paper is to investigate the opinions of Iranian users on the Twitter social network about cryptocurrencies and provide the best model for classifying tweets based on sentiment. In the case of automatic analysis of tweets, managers and officials in the field of economy can gain knowledge from the general public's point of view about this issue and use the information obtained in order to properly manage this phenomenon. For this purpose, in this paper, in order to build emotion classification models, natural language processing techniques such as bag of words (BOW) and FastText for text vectorization and classical machine learning algorithms including KNN, SVM and Adaboost learning methods Deep including LSTM and BERT model were used for classification, and finally BERT linguistic model had the best accuracy with 83.50%.

cs.CL↗

arXiv2019

The Star Formation History and Dynamics of the Ultra-diffuse Galaxy Dragonfly 44 in MOND and MOG

The observed line-of-sight velocity dispersion $σ_{los}$ of the ultra diffuse galaxy Dragonfly 44 (DF44) requires a Newtonian dynamical mass-to-light ratio of $M_{dyn}/L_I=26^{+7}_{-6}$ Solar units. This is well outside the acceptable limits of our stellar population synthesis (SPS) models, which we construct using the integrated galactic initial mass function (IGIMF) theory. Assuming DF44 is in isolation and using Jeans analysis, we calculate $σ_{los}$ profiles of DF44 in Milgromian dynamics (MOND) and modified gravity (MOG) theories without invoking dark matter. Comparing with the observed kinematics, the best-fitting MOND model has $M_{dyn}/L_I = 3.6_{-1.2}^{+1.6}$ and a constant orbital anisotropy of $β=-0.5_{-1.6}^{+0.4}$. In MOG, we first fix its two theoretical parameters $α$ and $μ$ based on previous fits to the observed rotation curve data of The HI Nearby Galaxy Survey (THINGS). The DF44 $σ_{los}$ profile is best fit with $M_{dyn}/L_I=7.4_{-1.4}^{+1.5}$, larger than plausible SPS values. MOG produces a $σ_{los}$ profile for DF44 with acceptable $M_{dyn}/L_I$ and isotropic orbits if $α$ and $μ$ are allowed to vary. MOND with the canonical $a_0$ can explain DF44 at the $2.40 σ$ confidence level (1.66\%) if considering both its observed kinematics and typical star formation histories in an IGIMF context. However, MOG is ruled out at $5.49 σ$ ($P$-value of $4.07 \times 10^{-8}$) if its free parameters are fixed at the highest values consistent with THINGS data.

astro-ph.GA↗

arXiv2016

Testing modified gravity with dwarf spheroidal galaxies

The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light ($M_*/L$) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion ($σ_{\emph{los}}$) of stars in eight MW dSphs in the context of the modified gravity (MOG) theory of Moffat, assuming a constant $M_*/L$ ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters $ α$ and $ μ$ of the theory to be constant as has already been inferred from fitting to the observed rotational data of The HI Nearby Galaxy Survey catalogue of galaxies. We find that the derived $M_*/L$ ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of the dSph with reasonable $M_*/L$ values, we must vary $α$ and $μ$ on a case by case basis. A common pair of values cannot be found for all dSphs. Comparing with the values found from rotation curve fitting, it appears that $μ$ correlates strongly with galaxy luminosity, shedding doubt on it as a universal constant.

astro-ph.GA↗

arXiv2016

Performance Enhancement of the Golden Code by Utilizing ORIOL Antenna

In this paper, a novel method is exposed to improve the performance of the Golden code, by using octagonal reconfigurable isolated orthogonal element (ORIOL) antennas, instead of a conventional microstrip patch antenna. The aforementioned antenna, should be employed in both the transmitter and the receiver sides, to approach the mentioned improvement. As a matter fact, in this paper, we recommend space-time-polarization diversity instead of space-time singly; therefore it is obvious that by employing the aforementioned technique, the system obtains more strength against destructive fading. The simulations for different rates have confirmed that, utilizing ORIOL antenna outperforms patch microstrip one, which is roughly about $2$ to $3$ dB, according to the rates.

cs.IT↗