Sharif Digital Repository

A prototype balloon-borne telescope is being constructed for γ-ray observations in the MeV energy range. The Tracking and Imaging Gamma-Ray Experiment (TIGRE) uses multi-layers of thin silicon detectors to track and measure the energy losses of Compton recoil electrons. When combined with the direction and energy of the Compton scattered γ-ray a unique incident direction for each photon event is determined. This facilitates background rejection, improved sensitivity and image reconstruction. The converter/tracker also serves as an electron-positron pair detector for γ-rays up to 100 MeV. The initial continental US flight will be used to determine the sub-orbital atmospheric backgrounds and... 

The population of nearby dwarf galaxies in the Local Group constitutes a complete galactic environment, perfect suited for studying the connection between stellar populations and galaxy evolution. In this study, we are conducting an optical monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify long period variable stars (LPVs). These stars are at the end points of their evolution and therefore their luminosity can be directly translated into their birth masses; this enables us to reconstruct the star formation history. By the end of the monitoring survey, we will have performed observations over ten epochs, spaced... 

The muon charge ratio contains important information about the flux of atmospheric neutrinos and the hadronic interactions. Using a cosmic ray telescope, the atmospheric muon charge ratio has been studied. The result of this experiment is compared with simulation results using the CORSIKA code. © 2019 Elsevier B.V  

We present a Vector Dark Matter (VDM) model that explains the 3.5 keV line recently observed in the XMM-Newton observatory data from galaxy clusters. In this model, dark matter is composed of two vector bosons, V and V', which couple to the photon through an effective generalized Chern-Simons coupling, gV. V' is slightly heavier than V with a mass splitting mV' - mV 3.5 keV. The decay of V' to V and a photon gives rise to the 3.5 keV line. The production of V and V' takes place in the early universe within the freeze-in framework through the effective gV coupling when mV' < T < Λ, Λ being the cut-off above which the effective gV coupling is not valid. We introduce a high energy model that... 

TIGRE, the UCR Compton gamma-ray telescope, is designed to make use of the Compton recoil electron track to improve the flux sensitivity in the medium gamma-ray energy range (0.4-100 MeV). TIGRE uses multilayers of silicon strip detectors to track Compton scattered electrons, and CsI detectors to measure the scattered photon energy and direction. In this work, using Monte-Carlo simulation, we show the improvement that can be obtained when the electron tracking feature is added to a conventional Compton telescope. In simulating a Crab-like source in a balloon-background environment, the flux sensitivity for TIGRE is enhanced by a factor of 2.5 and the source location accuracy by a factor 3... 

We discuss the prospect of extracting the values of the mixing parameters δ and θ13 through the detection of cosmic neutrinos in the planned and forthcoming neutrino telescopes. We take the ratio of the μ-track to shower-like events, R, as the realistic quantity that can be measured in the neutrino telescopes. We take into account several sources of uncertainties that enter the analysis. We then examine to what extent the deviation of the initial flavor composition from we : w μ : wτ 1 : 2 : 0 can be tested  

A cosmic ray tracking telescope has been made for the measurement of the secondary cosmic ray flux at ground level. The observations have been made both looking in the direction of the sun and away from the sun. Our observations by the telescope shows a deficiency in the detected number of cosmic rays entering the telescope when its axis was pointing to the sun compared to that entering the telescope with no sun in its field of view. The statistical significance of this deficit with the Li and Ma method stands near 1.3σ for all of our observations. © 2016 Elsevier B.V  

A cosmic ray telescope consisting of two scintillators (each one with a surface area of 0.14 m2, spaced 283 cm top of each other) was constructed to study the angular distribution of atmospheric muons. Using the CORSIKA code, the muons energy spectrum is parameterized in different energy regions at Tehran's altitude (1200 m above sea level ≡897 gcm−2), and by using a Monte Carlo program, the minimum energy recorded by the telescope is calculated. Due to the geomagnetic field, in the azimuth angle distribution of atmospheric muons, an anisotropy is observed in the East–West direction. The zenith angle distribution of the atmospheric muons follows the function cosnθ. Due to the relatively... 

Aims. Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected on a longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. The aim of the study described in this paper is to fully simulate the scintillation process, starting from the molecular cloud description as a fractal object, ending with the simulations of fluctuating stellar light curves. Methods. Fast Fourier transforms are first used to simulate fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated... 

We report follow-up observations of 477 program Near-Earth Asteroids (NEAs) using nine telescopes of the EURONEAR network having apertures between 0.3 and 4.2 m. Adding these NEAs to our previous results we now count 739 program NEAs followed-up by the EURONEAR network since 2006. The targets were selected using EURONEAR planning tools focusing on high priority objects. Analyzing the resulting orbital improvements suggests astrometric follow-up is most important days to weeks after discovery, with recovery at a new opposition also valuable. Additionally we observed 40 survey fields spanning three nights covering 11 square degrees near opposition, using the Wide Field Camera on the 2.5 m... 

The charge ratio of cosmic muons has important information in both "the atmospheric neutrinos anomaly" and "the hadronic interactions". We measured the muon charge ratio (Rμ = N μ+/Nμ-) in the cosmic rays flux at the momenta range 0.76-1.60 GeV/c at Sharif University of Technology in Tehran (35°43′N, 51°20′E) and 1200 m above sea level (890 gcm -2) by using a cosmic ray telescope. We used the delayed coincidence method based on reduced mean life time of negative muon due to nuclear capture in matter. By finding Rμ in different time intervals, we indicated 3 week time interval is proper to obtain Rμ and in this time interval, Rμ = 1.18±0.03. So we compared the experimental data to predictions... 

An experiment has been developed for the measurement of the muon charge ratio (ratio of positive to negative muons) in the cosmic ray flux in energy range 0.236-0.242 GeV. The muon charge ratio is found to be 1.35 ± 0.10 with a mean zenith angle of 32° ± 5°. Meanwhile, the distributions of muons in zenith (θ) and azimuth angles have been studied. A cosnθ distribution with n = 1.95 ± 0.13 has been obtained. An asymmetry has been observed in East-West directions because of geomagnetic field. © 2005 Elsevier B.V. All rights reserved  

Various models for the Galactic distribution of massive compact halo objects (MACHOs) have been proposed for the interpretation of microlensing toward the Large Magellanic Cloud (LMC). A direct way to fit the best model is by measuring the lens parameters, which can be obtained by measuring the Einstein crossing time and the parallax effect on the microlensing light curve and by astrometry of centroids of images. In this work, the theoretical distribution of these parameters is obtained for the various power-law Galactic dark halo models and MACHO mass functions (MF). For self-lensing as one of the models for the interpretation of LMC events, the maximum shift of image centroids and the... 

Aims. Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected at a longer time scale when the light of remote stars crosses an interstellar molecular cloud, but it has never been observed at optical wavelength. In a favorable case, the light of a background star can be subject to stochastic fluctuations on the order of a few percent at a characteristic time scale of a few minutes. Our ultimate aim is to discover or exclude these scintillation effects to estimate the contribution of molecular hydrogen to the Galactic baryonic hidden mass. This feasibility study is a pathfinder toward an observational strategy to search for scintillation, probing... 

A feasible and low cost approach to implement a nonplanar dual-polarized log-periodic dipole array antenna using printed circuit board (PCB) technology is proposed. The proposed antenna utilizes a very short transition from a coaxial cable to a balanced twin-lead transmission line to realize an ultrawide bandwidth balun, and has two distinct scaling factor values for high and low frequency elements. A prototype of the antenna operating over the frequency range of 1-13 GHz was designed, fabricated, and tested. An average gain of 7 dBi is obtained. Measured VSWR, cross-polarization and front-to-back ratio are better than 2.6, -16 dB, and 22 dB, respectively  

In this study, a novel type of passive energy dissipation device called a Telescopic Lead Yielding Damper (TLYD) is proposed and analyzed. This device comprises co-axial steel cylinders and lead rings, such that these rings act as shear locks between the steel cylinders. TLYDs dissipate energy through the plastic shear deformation of lead metal. The telescopic mechanism used in TLYDs allows these small-sized dampers to tolerate large axial displacements with low fatigue. For each telescopic level, a yield plateau is added to the hysteresis behavior of TLYD devices. Each yield plateau resists a different performance level, namely design-based and maximum credible earthquakes. Seven...