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STARS AS GRAVITATIONAL WAVE DETECTORS
KHOSROSHAHI H. G.,SOBOUTI Y. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
In attempts to detect gravitational waves, the response of some celestial systems such as the earth[l] or binary systems[2] to such waves have been investigated. Following this line of thought, here we study the possibility of excitation of the oscillation modes of a polytropic star by gravitational radiation and calculate the relevant absorption cross sections.
Rouhollah Khosroshahi,Nastaran A. Tehrani,Mozhdeh Forouzandeh,Fatemeh Behrouznejad,Nima Taghavinia,Mojtaba Bagherzadeh 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.106 No.-
In this work, synthesis of CuIn0.75Ga0.25S2 (CIGS) nanoparticles, the formation of stable dispersion, depositionof high-quality films and, fabrication of thin-film Perovskite solar cells are reported. The stability ofnanoparticle ink is crucial in the formation of device-quality films. The chalcogenide-based materials arewidely used in thin-film solar cells; in particular, Cu(In,Ga)S2 are used as an absorber and hole transportinglayer. In the present study, the nanoparticles of about 20 nm size and bandgap of 1.5 eV are synthesizedusing a heat-up method. A variety of solvents are used as dispersing media and the stability of theinks is evaluated by precise optical monitoring. We observe a clear dependence of ink stability to thepolarity index of the solvent, where the best stability occurs at a polarity index of about 0.26–0.36, correspondingto a range of solvents including chloroform. The thin films that are spin-coated using CIGSchloroform ink show large cracks, presumably due to the high vapor pressure of chloroform andevaporation-induced stress in the film. We resolve this problem through low-temperature deposition,which resulted in highly uniform pin-hole and crack-free films. Finally, the optimum deposition conditionis used to fabricate perovskite solar cells having about 16.5% efficiency with CIGS as a hole transportlayer.
PROBING GALAXY FORMATION MODELS IN COSMOLOGICAL SIMULATIONS WITH OBSERVATIONS OF GALAXY GROUPS
HABIB. G., KHOSROSHAHI,GOZALIASL, GHASSEM,FINOGUENOV, ALEXIS,RAOUF, MOJTABA,MIRAGHEE, HALIME The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We use multi-wavelength observations of galaxy groups to probe the formation models for galaxy formation in cosmological simulations, statistically. The observations include Chandra and XMM-Newton X-ray observations, optical photometry and radio observations at 1.4 GHz and 610 MHz. Using a large sample of galaxy groups observed by the XMM-Newton X-ray telescope as part of the XMM-Large Scale Survey, we carried out a statistical study of the redshift evolution of the luminosity gap for a well defined mass-selected group sample and show the relative success of some of the semi-analytic models in reproducing the observed properties of galaxy groups up to redshift z ~ 1.2. The observed trend argues in favour of a stronger evolution of the feedback from active galactic nuclei at z < 1 compared to the models. The slope of the relation between the magnitude of the brightest cluster galaxy and the value of the luminosity gap does not evolve with redshift and is well reproduced by the models. We find that the radio power of giant elliptic galaxies residing in galaxy groups with a large luminosity gap are lower compared to giant ellipticals of the same stellar masses but in typical galaxy groups.
GROUPS OF GALAXIES IN HISTORY: EVOLUTION IN THE MILLENNIUM SIMULATION
HASHEMIZADEH, ABDOLHOSEIN,KHOSROSHAHI, HABIB G.,RAOUF, MOJTABA,NEZHAD, ALIREZA MOLAEI The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We use the millennium simulation for studying the evolution of groups of galaxies over time. We find fossil and non-fossil groups as well as old and young groups at redshift z = 0 and follow them back in time to investigate the evolution of their parameters, such as mass assembly, luminosity gap and halo mass concentration. We find that fossils assemble a larger fraction of their mass at z = 0 than controls. The magnitude gaps between fossil and non-fossil groups are not the same because of major and minor mergers, in old and young groups as well. We also find that WMAP1 and WMAP7 cosmologies lead to the same evolutionary history for fossil and control groups.
AGE DATING GALAXY GROUPS IN THE MILLENNIUM SIMULATION
RAOUF, MOJTABA,KHOSROSHAHI, HABIB G. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We study galaxies drawn from the semi-analytic models of Guo et al. (2011) based on the Millennium Simulation. We establish a set of four observationally measurable parameters which can be used in combination to identify a subset of galaxy groups which are old, with a very high probability. We therefore argue that a sample of fossil groups selected based on the luminosity gap will result in a contaminated sample of old galaxy groups. By adding constraints on the luminosity of the brightest galaxy, and its offset from the group luminosity centroid, we can considerably improve the age-dating.
Javad Tavakoli,Mohammad E. Khosroshahi 대한의용생체공학회 2018 Biomedical Engineering Letters (BMEL) Vol.8 No.3
The surface properties of implant are responsible to provide mechanical stability by creating an intimate bond between thebone and implant; hence, play a major role on osseointegration process. The current study was aimed to measure surfacecharacteristics of titanium modified by a pulsed Nd:YAG laser. The results of this study revealed an optimum density oflaser energy (140 Jcm-2), at which improvement of osteointegration process was seen. Significant differences were foundbetween arithmetical mean height (Ra), root mean square deviation (Rq) and texture orientation, all were lower for140 Jcm-2 samples compared to untreated one. Also it was identified that the surface segments were more uniformlydistributed with a more Gaussian distribution for treated samples at 140 Jcm-2. The distribution of texture orientation athigh laser density (250 and 300 Jcm-2) were approximately similar to untreated sample. The skewness index that indicateshow peaks and valleys are distributed throughout the surface showed a positive value for laser treated samples, compared tountreated one. The surface characterization revealed that Kurtosis index, which tells us how high or flat the surface profileis, for treated sample at 140 Jcm-2 was marginally close to 3 indicating flat peaks and valleys in the surface profile.
SUSTAINING GALAXY EVOLUTION: THE ROLE OF STELLAR FEEDBACK
JAVADI, ATEFEH,VAN LOON, JACCO TH.,KHOSROSHAHI, HABIB The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group galaxy M33. The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The pulsating giant stars (AGB and red supergiants) are identified and their distributions are used to derive the star formation rate as a function of age. These stars are also important dust factories; we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. The mass-loss rates are seen to increase with increasing strength of pulsation and with increasing bolometric luminosity. Low-mass stars lose most of their mass through stellar winds, but even super-AGB stars and red superginats lose ~40% of their mass via a dusty stellar wind. We construct a 2-D map of the mass-return rate, showing a radial decline but also local enhancements due to agglomerations of massive stars. By comparing the current star formation rate with total mass input to the ISM, we conclude that the star formation in the central regions of M33 can only be sustained if gas is accreted from further out in the disc or from circum-galactic regions.
Advanced Cascade Multilevel Converter with Reduction in Number of Components
Ajami, Ali,Oskuee, Mohammad Reza Jannati,Mokhberdoran, Ataollah,Khosroshahi, Mahdi Toupchi The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.1
In this paper a novel converter structure based on cascade converter family is presented. The suggested multilevel advanced cascade converter has benefits such as reduction in number of switches and power losses. Comparison depict that proposed topology has the least number of IGBTs among all multilevel cascade type converters which have been introduced recently. This characteristic causes low cost and small installation area for suggested converter. The number of on state switches in current path is less than conventional topologies and so the output voltage drop and power losses are decreased. Symmetric and asymmetric modes are analyzed and compared with conventional multilevel cascade converter. Simulation and experimental results are presented to illustrate validity, good performance and effectiveness of the proposed configuration. The suggested converter can be applied in medium/high voltage and PV applications.
Advanced Cascade Multilevel Converter with Reduction in Number of Components
Ali Ajami,Mohammad Reza Jannati Oskuee,Ataollah Mokhberdoran,Mahdi Toupchi Khosroshahi 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.1
In this paper a novel converter structure based on cascade converter family is presented. The suggested multilevel advanced cascade converter has benefits such as reduction in number of switches and power losses. Comparison depict that proposed topology has the least number of IGBTs among all multilevel cascade type converters which have been introduced recently. This characteristic causes low cost and small installation area for suggested converter. The number of on state switches in current path is less than conventional topologies and so the output voltage drop and power losses are decreased. Symmetric and asymmetric modes are analyzed and compared with conventional multilevel cascade converter. Simulation and experimental results are presented to illustrate validity, good performance and effectiveness of the proposed configuration. The suggested converter can be applied in medium/high voltage and PV applications.