arXiv subjects

Majid Bahraminasr

Publications and source records attributed to Majid Bahraminasr.

6 recordsLinked to original sources

arXiv2026

Insights into the electrorheological and electrohydrodynamic regimes in electrically driven emulsion

Recently, we reported the electrorheoimaging (ERI) technique (Bahraminasr et al, 2026), and found that frequency-dependent electric field of an oil-in-oil emulsion yields two distinct regimes: a high-frequency dipolar, electrorheological (ER) regime and a low-frequency electrohydrodynamic (EHD) regime. In this work, we identify a phenomenological model to fit the results in the ER regime to a classic yield-stress fluid, and find collapse onto a master curve upon rescaling, consistent with a yield stress that grows approximately as $E^2$. Macroscopic small-amplitude oscillatory shear (SAOS) rheology is compared with passive microrheology employing differential dynamic microscopy (DDM), with the close agreement implying scale independence of the ER behaviour, and indicating that, unlike steady shear, SAOS measurements do not restructure these samples and probe underlying material properties. Finally, under the presence of both steady shear and electric fields in the EHD regime, the emulsion forms banded structures composed of alternating droplet-rich and droplet-depleted regions. We explore recurrence and divergence in the location of these bands: they emerge within seconds of field application and decay rapidly after the field is switched off. Using the Jensen--Shannon divergence between radial intensity profiles, we show that the driven structure loses memory on timescales of order $1~s$ commensurate with the timescale of the EHD convection roll. For much longer field-off intervals successive banding events become statistically independent.

cond-mat.soft↗

arXiv2026

Tunable turbulence in driven microscale emulsions

We present a tunable, non-equilibrium oil-in-oil emulsion that serves as a model system for investigating the transition from controlled droplet deformation to multiscale flows reminiscent of turbulence. By utilizing a miscible mixture of silicone and motor oils as the continuous phase and the immiscible castor oil as the droplet phase, we isolate electrical conductivity as a single experimental control parameter, varying it by over two orders of magnitude while keeping viscosity and permittivity nearly constant. This high degree of control allows us to systematically traverse the electrohydrodynamic (EHD) phase diagram with dielectric constant and conductivity as control parameters. We validate small-deformation theory at low fields before driving the system into a regime of multiscale, unsteady flows at high fields. We employ three complementary approaches on the same system (particle image velocimetry (PIV), used to map velocity fields, and rheometry and differential dynamic microscopy (DDM), two techniques used to probe viscosity and diffusion) to quantify the emergence of scale invariance in the energy spectra with increasing field strength. Above a threshold field, we find that the spatio-temporal energy spectra obtained by PIV analysis of droplet dynamics display power-law scaling, $E(k) \sim k^{-α_k}$, where $α_k$ approaches the inertial turbulence exponent of $5/3$ at high fields. Energy spectra from rheometry also yield a power law, $S(ν) \sim ν^{-α_ν}$, with $α_ν= 5/3$ at high fields. Mean square displacement (MSD) analyses on the same datasets reveal super-diffusive behavior, $\mathrm{MSD} \sim t^γ$, with $γ= 3/2$. These observations provide strong evidence of a conductivity-tunable transition to EHD-driven turbulence in a microscale emulsion.

cond-mat.soft↗

arXiv2021

Study of Pluto's Atmosphere Based on 2020 Stellar Occultation Light Curve Results

On 6 Jun 2020, Pluto's stellar occultation was successfully observed at a ground-based observatory and Pluto's atmospheric parameters were investigated. We used an atmospheric model of Pluto (DO15), assuming a spherical and transparent pure N2 atmosphere. Using ray-tracing code the stellar occultation light curve was satisfactorily fitted to this model. We found that Pluto's atmospheric pressure at the reference radius of 1215 km is 6.72+_0.21 μbar. Our estimated pressure shows a continuation of the increasing pressure studied in 2016 consistent with a seasonal volatile transport model. We concluded that the N2 condensation processes in the Sputnik Planitia glacier are increasing due to the heating of the N2 ice in this basin. This study's result was shown on the diagram of the annual evolution of atmospheric pressure.

astro-ph.EP↗

arXiv2021

Sensitivities to secret neutrino interaction at FASER$ν$

We study the impact of the coupling of neutrinos with a new light neutral gauge boson, $Z^\prime$, with a mass of less than 500 {\rm MeV} in FASER$ν$ experiment. Scenarios in which a light gauge boson is coupled to neutrinos are motivated within numerous contexts which are designed to explain various anomalies in particle physics and cosmology. This interaction leads to a new decay mode for charged mesons to a light lepton plus neutrino and $Z^{\prime}$, ($π^+(K^+)\to e^+ νZ^\prime$) followed by the subsequent decay of $Z^\prime$ into the pair of neutrino and anti-neutrino, ($Z^\prime \to ν\barν$). FASER$ν$, the Forward Search Experiment at the LHC, has the potential to detect collider neutrinos for the first time. In particular, the FASER$ν$ emulsion detector will provide the opportunity to detect $τ$-neutrinos and to measure their energies. Using this ability of FASER$ν$ emulsion detector, we investigate the potential of FASER$ν$ experiment and the proposed upgraded version of this experiment, FASER2$ν$, to constrain the coupling of a neutrino with the light gauge boson.

hep-ph↗

arXiv2020

Evaluating the Effect of Four Unknown Parameters Included in a Latitudinal Energy Balance Model on the Habitability of Exoplanets

Among different models for determining the habitable zone (HZ) around a star, a Latitudinal Energy Balance Model (LEBM) is very beneficial due to its parametricity which keeps a good balance between complexity and simulation time. This flexibility makes the LEBM an excellent tool to assess the impact of some key physical parameters on the temperature and the habitability of a planet. Among different physical parameters, some of them, up until now, cannot be determined by any method such as the planet's spin obliquity, diurnal period, ocean-land ratio, and pressure level. Here we apply this model to study the effect of these unknown parameters on the habitability of three exoplanets located in the inner, outer, and middle of their optimistic HZ. Among the examined parameters, the impact of pressure is more straightforward. It has a nearly direct relation with temperature and also with the habitability in the case of a cold planet. The effect of other parameters is discussed with details. To quantify the impact of all these unknown parameters we utilize a statistical interface which provides us with the conditional probability on habitability status of each planet.

astro-ph.EP↗

arXiv2020

A Guide for CosmoMC Installation and Running

CosmoMC is a Cosmological Monte Carlo package that explores parameter space, finds the best-fit values, and makes contour plots for various observational data. The present manual assists you with the installation steps and running of CosmoMC. Also, we briefly explain Markov chains analysis and generating plots and tables for the parameters. This guide is for everyone who is not familiar with GNU/Linux and wants to install and run CosmoMC for the first time.

astro-ph.IM↗