Dissecting the Compton scattering kernel I: Isotropic media

Compton scattering between electrons and photons plays a crucial role in astrophysical plasmas. Many important aspects of this process can be captured by using the so-called Compton scattering kernel. For isotropic media, exact analytic expressions (valid at all electron and photon energies) do exist but are hampered by numerical issues and often are presented in complicated ways. In this paper, we summarize, simplify and improve existing analytic expressions for the Compton scattering kernel, with an eye on clarity and physical understanding. We provide a detailed overview of important properties of the kernel covering a wide range of energies and highlighting aspects that have not been appreciated as much previously. We discuss analytic expressions for the moments of the kernel, comparing various approximations and demonstrating their precision. We also illustrate the properties of the scattering kernel for thermal electrons at various temperatures and photon energies, introducing new analytic approximations valid to high temperatures. The obtained improved formulae for the kernel and its moments should prove useful in many astrophysical computations, one of them being the evolution of spectral distortions of the cosmic microwave background in the early Universe. A novel code, CSpack, for efficient computations of the Compton scattering kernel and its properties (in the future also including anisotropies in the initial electron and photon distributions) is being developed in a series of papers and will be available within one month.Comment: Significantly edited based on the referee's comments. 18 pages + 3 pages appendix, 17 figures. Accepted for publication in MNRA

Strain-induced stabilization of Al functionalization in graphene oxide nanosheet for enhanced NH3 storage

Strain effects on the stabilization of Al ad-atom on graphene oxide(GO)nanosheet as well as its implications for NH3 storage have been investigated using first-principles calculations.The binding energy of Al ad-atom on GO is found to be a false indicator of its stability.Tensile strain is found to be very effective in stabilizing the Al ad-atom on GO.It strengthens the C-O bonds through an enhanced charge transfer from C to O atoms. Interestingly,C-O bond strength is found to be the correct index for Al's stability.Optimally strained Al-functionalized GO binds up to 6 NH3 molecules,while it binds no NH3 molecule in unstrained condition.Comment: 11 pages, 3 figures, 4 tables, Applied Physics Letters (Under Review

Polylithiated (OLi2) functionalized graphane as a potential hydrogen storage material

Hydrogen storage capacity, stability, bonding mechanism and the electronic structure of polylithiated molecules (OLi2) functionalized graphane (CH) has been studied by means of first principle density functional theory (DFT). Molecular dynamics (MD) have confirmed the stability, while Bader charge analysis describe the bonding mechanism of OLi2 with CH. The binding energy of OLi2 on CH sheet has been found to be large enough to ensure its uniform distribution without any clustering. It has been found that each OLi2 unit can adsorb up to six H2 molecules resulting into a storage capacity of 12.90 wt% with adsorption energies within the range of practical H2 storage application.Comment: 11 pages, 4 figures, 1 table, Phys. Chem. Chem. Phys. (submitted

Strain induced lithium functionalized graphane as a high capacity hydrogen storage material

Strain effects on the stability, electronic structure, and hydrogen storage capacity of lithium-doped graphane (CHLi) have been investigated by stateof-the art first principle density functional theory (DFT). Molecular dynamics MD) simulations have confirmed the stability of Li on graphane sheet when it is subject to 10% of tensile strain. Under biaxial asymmetric strain, the binding energy of Li of graphane (CH) sheet increases by 52% with respect to its bulk's cohesive energy. With 25% doping concentration of Li on CH sheet,the gravimetric density of hydrogen storage is found to reach up to 12.12wt%. The adsorption energies of H2 are found to be within the range of practical H2 storage applications.Comment: 13 pages, 7 figures, 1 table, Applied Physics Letters (Under Review

A 50-year-old woman presented with severe reduction of vision and recurrent pain in right eye following cataract surgery

This article has no abstract. The first 100 words appear below: A 50-year-old female, hailing from Patuakhali, was admitted at the Department of Ophthalmology for the management of severe reduction of vision and pain at the right eye for the last 7 months following cataract surgery at a government hospital. Her cataract surgery (small incision cataract surgery with PC-IOL implantation) of the right eye was performed on October 28, 2018. On the first post-operative day, she developed pain, redness and severe reduction of vision in the right eye. The following day, she was discharged with the advice of some medications like moxifloxacin, dexamethasone, bromfenac eye drops and oral acetazolamide and potassium

Comparison of the full-potential and frozen-core approximation approaches to density-functional calculations of surfaces

We scrutinize the accuracy of the pseudopotential approximation in density-functional theory (DFT) calculations of surfaces by systematically comparing to results obtained within a full-potential setup. As model system we choose the CO oxidation at a RuO2(110) surface and focus in particular on the adsorbate binding energies and reaction barriers as target quantities for the comparison. Rather surprisingly, the major reason for discrepancy does not result from the neglected semi-core state relaxation in the frozen-core approximation, but from an inadequate description of the local part of the Ru pseudopotential, responsible for the scattering of f like waves. Tiny, seemingly irrelevant, imprecisions appearing in these properties can have a noticeable influence on the surface energetics. At least for the present example, we obtain excellent agreement between both approaches, if the pseudopotential describes these scattering properties accurately.Comment: 8 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Effects of temperature and adsorbates on the composition profile of Pt-Rh nanocatalysts : A comparative study

Monte-Carlo simulation technique has been used to investigate the effect of temperature and adsorbed gases on the composition profile of unsupported Pt-Rh nanocatalysts. For a 2406 atom fcc cubo-octahedral Pt$_{\rm{}50}$Rh$_{\rm{}50}$ nanocatalyst the shell-wise composition for all the eight shells has been simulated. For the temperatures 700 K, 1000 K and 1300 K, the top shell of clean Pt-Rh nanocatalysts is found to be mildly Pt-enriched, while the second shell is Pt-depleted. The Pt concentration of the top shell shows a maximum at T = 1000 K. In presence of a quarter monolayer of adsorbed oxygen the top shell shows Rh enrichment, while all the other shells show Pt-enrichment. This is true for all the three temperatures for which the composition profiles have been studied.Comment: 9 pages (LATEX), 4 postscript figures ; Accepted for publication in Physica

Heavy quark energy loss and D-Mesons at RHIC and LHC energies

We obtain the radiative energy loss of a heavy quark in a deconfined medium due to radiation of gluons off them using a recently derived generalised gluon emission spectrum. We find that the heavy flavour loses energy almost in a similar fashion like light quarks through this process. With this, we further analyse the nuclear modification factor for D-meson at LHC and RHIC energies. In particular, the obtained result is found to be in close agreement with the most recent data from ALICE collaboration at 2.76 ATeV Pb-Pb collisions. We also discuss the nuclear modification factor due to the collisional energy loss. Furthermore, the result of non-photonic single electron from the decay of both D and B mesons is compared with the RHIC data at 200 AGeV Au-Au collisions, which is also in close agreement.Comment: Non-photonic single electron results included, title changed a bit, version accepted in Phys. Lett.