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Analytical and semi-analytical solutions to the kinetic equation with Coulomb collision term and a monoenergetic source function  [PDF]
P. R. Goncharov
Physics , 2010, DOI: 10.1063/1.3505482
Abstract: Complete and physically adequate analytical and semi-analytical solutions have been obtained using a practical dimensionless form of kinetic equation assuming azimuthal symmetry and Maxwellian distributions of target plasma species. Formerly considered simplified equations with truncated Coulomb collision term do not conserve the number of particles, are inapplicable to describe high energy distribution tails, and are also essentially unable to demonstrate the Maxwellization process naturally observed in the low energy region of correct distributions. The results may be useful in numerical modeling and in experimental data analysis, especially concerning nuclear processes and advanced localized, angle-resolved suprathermal particle diagnostics.
Study of wavelength dependence of mode instability based on a semi-analytical model  [PDF]
Rumao Tao,Pengfei Ma,Xiaolin Wang,Pu Zhou,Zejin Liu
Physics , 2015, DOI: 10.1109/JQE.2015.2442760
Abstract: We present theoretical study of wavelength dependence of mode instability (MI) in high power fiber lasers, which employs an improved semi-analytical theoretical model. The influence of pump / seed wavelength and photodarkening on threshold has been studied. The results indicate promising MI suppression through pumping or seeding at an appropriate wavelength. Small amounts of photodarkening can lead to significant impact on MI.
Semi-analytical approach to short-wavelength dispersion and modal properties of photonic crystal fibers  [PDF]
Niels Asger Mortensen
Physics , 2005, DOI: 10.1364/OL.30.001455
Abstract: We consider photonic crystal fibers made from arbitrary base materials and derive a unified semi-analytical approach for the dispersion and modal properties which applies to the short-wavelength regime. In particular we calculate the dispersion and the effective index and comparing to fully-vectorial plane wave simulations we find excellent agreement. We also calculate asymptotic results for the mode-field diameter and the V-parameter and from the latter we predict that the fibers are endlessly single mode for a normalized air-hole diameter smaller than 0.42, independently of the base material.
Galaxy stellar mass assembly: the difficulty matching observations and semi-analytical predictions  [PDF]
Morgane Cousin,Guilaine Lagache,Matthieu Bethermin,Jeremy Blaizot,Bruno Guiderdoni
Physics , 2014, DOI: 10.1051/0004-6361/201323062
Abstract: Semi-analytical models (SAMs) are currently the best way to understand the formation of galaxies within the cosmic dark-matter structures. While they fairly well reproduce the local stellar mass functions, correlation functions and luminosity functions, they fail to match observations at high redshift (z > 3) in most cases, particularly in the low-mass range. The inconsistency between models and observations indicates that the history of gas accretion in galaxies, within their host dark-matter halo, and the transformation of gas into stars, are not well followed. Hereafter, we briefly present a new version of the GalICS semi-analytical model. We explore the impacts of classical mechanisms, such as supernova feedback or photoionization, on the evolution of the stellar mass assembly. Even with a strong efficiency, these two processes cannot explain the observed stellar mass function and star formation rate distribution and some other relations. We thus introduce an ad-hoc modification of the standard paradigm, based on the presence of a \textit{no-star-forming} gas component, and a concentration of the star-forming gas in galaxy discs. The main idea behind the existence of the no-star-forming gas reservoir is that only a fraction of the total gas mass in a galaxy is available to form stars. The reservoir generates a delay between the accretion of the gas and the star formation process. This new model is in much better agreement with the observations of the stellar mass function in the low-mass range than the previous models, and agrees quite well with a large set of observations, including the redshift evolution of the specific star formation rate. However, it predicts a large fraction of no-star-forming baryonic gas, potentially larger than observed, even if its nature has still to be examined in the context of the missing baryon problem.
The Star Formation and AGN luminosity relation: Predictions from a semi-analytical model  [PDF]
Thales A. Gutcke,Nikos Fanidakis,Andrea V. Macciò,Cedric Lacey
Physics , 2015, DOI: 10.1093/mnras/stv1205
Abstract: In a Universe where AGN feedback regulates star formation in massive galaxies, a strong correlation between these two quantities is expected. If the gas causing star formation is also responsible for feeding the central black hole, then a positive correlation is expected. If powerful AGNs are responsible for the star formation quenching, then a negative correlation is expected. Observations so far have mainly found a mild correlation or no correlation at all (i.e. a flat relation between star formation rate (SFR) and AGN luminosity), raising questions about the whole paradigm of "AGN feedback". In this paper, we report the predictions of the GALFORM semi-analytical model, which has a very strong coupling between AGN activity and quenching of star formation. The predicted SFR-AGN luminosity correlation appears negative in the low AGN luminosity regime, where AGN feedback acts, but becomes strongly positive in the regime of the brightest AGN. Our predictions reproduce reasonably well recent observations by Rosario et al., yet there is some discrepancy in the normalisation of the correlation at low luminosities and high redshifts. Though this regime could be strongly influenced by observational biases, we argue that the disagreement could be ascribed to the fact that GALFORM neglects AGN variability effects. Interestingly, the galaxies that dominate the regime where the observations imply a weak correlation are massive early-type galaxies that are subject to AGN feedback. Nevertheless, these galaxies retain high enough molecular hydrogen contents to maintain relatively high star formation rates and strong infrared emission.
A Semi-Analytical Model of Visible-Wavelength Phase Curves of Exoplanets and Applications to Kepler-7 b and Kepler-10 b  [PDF]
Renyu Hu,Brice-Olivier Demory,Sara Seager,Nikole Lewis,Adam P. Showman
Physics , 2015, DOI: 10.1088/0004-637X/802/1/51
Abstract: Kepler has detected numerous exoplanet transits by precise measurements of stellar light in a single visible-wavelength band. In addition to detection, the precise photometry provides phase curves of exoplanets, which can be used to study the dynamic processes on these planets. However, the interpretation of these observations can be complicated by the fact that visible-wavelength phase curves can represent both thermal emission and scattering from the planets. Here we present a semi-analytical model framework that can be applied to study Kepler and future visible-wavelength phase curve observations of exoplanets. The model efficiently computes reflection and thermal emission components for both rocky and gaseous planets, considering both homogeneous and inhomogeneous surfaces or atmospheres. We analyze the phase curves of the gaseous planet Kepler-7 b and the rocky planet Kepler-10 b using the model. In general, we find that a hot exoplanet's visible-wavelength phase curve having a significant phase offset can usually be explained by two classes of solutions: one class requires a thermal hot spot shifted to one side of the substellar point, and the other class requires reflective clouds concentrated on the same side of the substellar point. The two solutions would require very different Bond albedos to fit the same phase curve; atmospheric circulation models or eclipse observations at longer wavelengths can effectively rule out one class of solutions, and thus pinpoint the albedo of the planet, allowing decomposition of the reflection and the thermal emission components in the phase curve. Particularly for Kepler-7 b, reflective clouds located on the west side of the substellar point can best explain its phase curve. We further derive that the reflectivity of the clear part of the atmosphere should be less than 7% and that of the cloudy part should be greater than 80% (abridged)
Collision Induced Galaxy Formation  [PDF]
C. Balland,J. Silk,R. Schaeffer
Physics , 1997, DOI: 10.1086/305470
Abstract: We present a semi-analytical model in which galaxy collisions and strong tidal interactions, both in the field and during the collapse phase of groups and clusters help determine galaxy morphology. From a semi-analytical analysis based on simulation results of tidal collisions (Aguilar & White 1985), we propose simple rules for energy exchanges during collisions that allow to discriminate between different Hubble types: efficient collisions result in the disruption of disks and substantial star formation, leading to the formation of elliptical galaxies; inefficient collisions allow a large gas reservoir to survive and form disks. Assuming that galaxy formation proceeds in a Omega_0=1 Cold Dark Matter universe, the model both reproduces a number of observations and makes predictions, among which are the redshifts of formation of the different Hubble types in the field. When the model is normalized to the present day abundance of X-ray clusters, the amount of energy exchange needed to produce elliptical galaxies in the field implies that they formed at z>2.5 while spiral galaxies formed at z<1.5. The model also offers a natural explanation for biasing between the various morphological types. We find that the present day morphology-density relation in the field is well reproduced under the collision hypothesis. Finally, predictions of the evolution of the various galaxy populations with redshift are made, in the field as well as in clusters.
Angular Intermittency and Analytical QCD Predictions  [PDF]
S. V. Chekanov
Physics , 1997,
Abstract: We present a comparison of local multiplicity fluctuations in angular phase-space intervals with first-order QCD predictions. The data are based on 810k hadronic events at 91.2 GeV collected with the L3 detector at LEP during 1994.
Predictions for Herschel from LambdaCDM: unveiling the cosmic star formation history  [PDF]
C. G. Lacey,C. M. Baugh,C. S. Frenk,A. J. Benson,A. Orsi,L. Silva,G. L. Granato,A. Bressan
Physics , 2009, DOI: 10.1111/j.1365-2966.2010.16463.x
Abstract: We use a model for the evolution of galaxies in the far-IR based on the LambdaCDM cosmology to make detailed predictions for upcoming cosmological surveys with the Herschel Space Observatory. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy SEDs including the reprocessing of radiation by dust. The model, which is the same as that in Baugh et al. (2005), assumes two different IMFs: a normal solar neighbourhood IMF for quiescent star formation in disks, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF appears necessary to explain the number counts and redshifts of faint sub-mm galaxies. In this paper, we present predictions for galaxy luminosity functions, number counts and redshift distributions in the Herschel imaging bands. We find that source confusion will be a serious problem in the deepest planned surveys. We also show predictions for physical properties such as star formation rates and stellar, gas and halo masses, together with fluxes at other wavelengths (from the far-UV to the radio) relevant for multi-wavelength follow-up observations. We investigate what fraction of the total IR emission from dust and of the high-mass star formation over the history of the Universe should be resolved by planned surveys with Herschel, and find a fraction ~30-50%, depending on confusion. Finally, we show that galaxies in Herschel surveys should be significantly clustered.
A Comparison between Semi-Analytic Model Predictions for the CANDELS Survey  [PDF]
Yu Lu,Risa H. Wechsler,Rachel S. Somerville,Darren Croton,Lauren Porter,Joel Primack,Peter S. Behroozi,Henry C. Ferguson,David C. Koo,Yicheng Guo,Mohammadtaher Safarzadeh,Kristian Finlator,Marco Castellano,Catherine E. White,Veronica Sommariva,Chris Moody
Physics , 2013, DOI: 10.1088/0004-637X/795/2/123
Abstract: We compare the predictions of three independently developed semi-analytic galaxy formation models that are being used to aid in the interpretation of results from the CANDELS survey. These models are each applied to the same set of halo merger trees extracted from the "Bolshoi" simulation and are carefully tuned to match the local galaxy stellar mass function using the powerful method of Bayesian Inference coupled with MCMC or by hand. The comparisons reveal that in spite of the significantly different parameterizations for star formation and feedback processes, the three models yield qualitatively similar predictions for the assembly histories of galaxy stellar mass and star formation over cosmic time. We show that the SAMs generally require strong outflows to suppress star formation in low-mass halos to match the present day stellar mass function. However, all of the models considered produce predictions for the star formation rates and metallicities of low-mass galaxies that are inconsistent with existing data and diverge between the models. We suggest that large differences in the metallicity relations and small differences in the stellar mass assembly histories of model galaxies stem from different assumptions for the outflow mass-loading factor. Importantly, while more accurate observational measurements for stellar mass, SFR and metallicity of galaxies at 1
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