Kamel A. K. Gadallah - Academia.edu (original) (raw)

Papers by Kamel A. K. Gadallah

$Research paper thumbnail of Analysis of the fractional relativistic polytropic gas sphere$

Scientific Reports

Many stellar configurations, including white dwarfs, neutron stars, black holes, supermassive sta... more Many stellar configurations, including white dwarfs, neutron stars, black holes, supermassive stars, and star clusters, rely on relativistic effects. The Tolman–Oppenheimer–Volkoff (TOV) equation of the polytropic gas sphere is ultimately a hydrostatic equilibrium equation developed from the general relativity framework. In the modified Riemann Liouville (mRL) frame, we formulate the fractional TOV (FTOV) equations and introduce an analytical solution. Using power series expansions in solving FTOV equations yields a limited physical range to the convergent power series solution. Therefore, combining the two techniques of Euler–Abel transformation and Padé approximation has been applied to improve the convergence of the obtained series solutions. For all possible values of the relativistic parameters ($$\sigma$$ σ ), we calculated twenty fractional gas models for the polytropic indexes n = 0, 0.5, 1, 1.5, 2. Investigating the impacts of fractional and relativistic parameters on the m...

Monthly Notices of the Royal Astronomical Society

The spectral energy distribution (SED) from the X-ray to far-IR is used to characterize active ga... more The spectral energy distribution (SED) from the X-ray to far-IR is used to characterize active galactic nuclei (AGNs) having obscuring dusty material. A sample of 73 AGNs, with redshifts of z < 2.5, is subdivided based on the optical spectra into subgroups of type 1 and 2 AGNs and no-AGN. The x-cigale code is used to produce the SEDs of these galaxies, fitting them with their observed flux densities. Accordingly, this code provides estimates of the physical properties, including the stellar mass, dust-to-gas mass ratio, far-UV attenuation, star-formation rate, and luminosity. All these properties and luminosity components, namely stellar, AGN, X-ray, and dust luminosities, are characterized versus the redshift. With the caveat that the sample is flux-limited and thus is affected by Malmquist bias, the results show that these properties increase as a function of redshift with various variation rates for each galaxy group, except for the far-UV attenuation of type 1 AGNs, which sho...

Applied Mathematics and Nonlinear Sciences, 2020

In this paper, we present a comprehensive analytical study on the perturbed restricted three bodi... more In this paper, we present a comprehensive analytical study on the perturbed restricted three bodies problem. We formulate the equations of motion of this problem, in the event of the asteroids belt perturbation. We find the locations of equilibrium points (collinear and triangular points) and analysis their linear stability. Furthermore the periodic orbits around both collinear and triangular points are found.

Advances in Space Research, 2015

The spectral changes of hydrogenated amorphous carbon (HAC) could show variable distributions of ... more The spectral changes of hydrogenated amorphous carbon (HAC) could show variable distributions of solid carbon abundance in the interstellar medium (ISM). The variable optical properties of HAC analogs, produced by the laser ablation in a high vacuum, depends on the variation in its atomic and electronic structures. The fraction of hydrogen atoms in HAC increases proportionally with the laser's power. The available solid carbon tied up in the interstellar HAC, being the carrier of the interstellar 3.4 lm and 4.6 lm À1 bands, is indicated by the strength of these bands. Comparing the strength of these bands with those of laboratory data indicates that the amount of carbon in HAC analogs is not inherently sufficient. The lack in the solid carbon (locked solid carbon) in these analogs can be analytically estimated to facilitate the simulation of cosmic carbon dust. The results show a reduction in the locked solid carbon when the fraction of hydrogen atoms in HAC analogs increases. When this fraction becomes approximately 0.52 relative to the total number of hydrogen and carbon atoms, there is no lack of carbon in HAC analogs. The interstellar distribution of variable solid carbon abundance is attributed to the modification of cosmic HAC, which occurs as a result of the variation in its hydrogen atom fraction and the UV processing taking place in the interstellar environments. This distribution reveals more solid carbon abundances reside in the dust phase and may assist in resolving the carbon crisis.

Physical chemistry chemical physics : PCCP, Jan 25, 2017

This work investigates the production of molecular hydrogen isotopologues (H2, HD, and D2) during... more This work investigates the production of molecular hydrogen isotopologues (H2, HD, and D2) during low energy electron irradiation of layered and isotopically labelled thin films of amorphous solid water (ASW) in ultrahigh vacuum. Experimentally, the production of these molecules with both irradiation time and incident electron energy in the range 400 to 500 eV is reported as a function of the depth of a buried D2O layer in an H2O film. H2 is produced consistently in all measurements, reflecting the H2O component of the film, though it does exhibit a modest reduction in intensity at the time corresponding to product escape from the buried D2O layer. In contrast, HD and D2 production exhibit peaks at times corresponding to product escape from the buried D2O layer in the composite film. These features broaden the deeper the HD or D2 is formed due to diffusion. A simple random-walk model is presented that can qualitatively explain the appearance profile of these peaks as a function of t...

Proceedings of The International Astronomical Union, 2011

UV processing of a hydrogenated amorphous carbon (HAC) may provide an interpretation of the inter... more UV processing of a hydrogenated amorphous carbon (HAC) may provide an interpretation of the interstellar UV bump at 4.6 mum-1 (217.5 nm) in the interstellar extinction curve. Mennella et al. (1996) had found that the UV irradiation of HAC materials has a strong effect creating a new absorption band which appears at 215 nm, attributing this band to %B i-%B i* electronic transitions in clusters of sp^2 hybridized carbon. We have irradiated HAC materials produced by laser ablation in H/He atmospheres with UV doses of up to 33% of the average interstellar dose. Structural investigation by electron microscopy reveals that these materials become more graphitic with UV irradiation. UV spectroscopy of the HACs shows that a stable UV bump appears at around 217 nm, which becomes stronger and narrower with increasing UV dose. The results are compared with the astronomical data of this band.

Astrophysics and Space Science, 2004

We investigated the chemical evolution in IC 63 nebula, a photo-dominated region (PDR). The chemi... more We investigated the chemical evolution in IC 63 nebula, a photo-dominated region (PDR). The chemical structure and the ionization state depend directly on the intensity of the incident UV radiation. The electron density is also affected by the incident UV radiation. It decreases gradually with the increase of the depth in the cloud varying from 5.9×10 −5 at the surface to 9.6×10 −9 in the core. Ionic carbon (C +) dominates the electron density in the outer region while ionic metals and other ions (H + , CH 2 D + , and HCO +) are the most dominant in the deepest region. Our results at A V = 6.7 mag are in good agreement with observations except in the case of H 2 S, where the calculated value is lower than the observed value by about two orders of magnitude.

Astronomy & Astrophysics, 2011

Context. Hydrogenated amorphous carbon (HAC) materials have been considered as a laboratory analo... more Context. Hydrogenated amorphous carbon (HAC) materials have been considered as a laboratory analog of cosmic carbonaceous nanoparticles in the interstellar medium (ISM). In the diffuse ISM, UV radiation can modify the electronic and atomic structure of HAC materials. Aims. Studying structural and optical properties of HAC materials in correlation with UV processing is very important to understand more clearly the effect of the UV radiation on carbonaceous dust grains in the diffuse ISM. This scenario can explain some astronomical spectral features such as the interstellar UV bump at 4.6 μm −1. Methods. Laser ablation has been used to produce nano-sized HAC materials which are subsequently irradiated by strong UV doses in a high vacuum. Transmission electron microscope images and spectroscopic analyses show the evolution of the internal structure of the material with the UV irradiation. Results. It is found that hydrogen content and the sp 3 /sp 2 hybridization ratio decrease with the UV irradiation. The graphene layers become longer in processed materials. Also, graphitic fibers are observed in modified materials. The variation in the internal structure leads to dramatic changes in the spectral properties in the FUV-VIS range. The UV irradiation of HAC materials, coresponding to 21-33% of the average dose of the UV radiation in diffuse ISM, has produced a new band centered at 4.6 μm −1 (217.5 nm). Conclusions. Consequently, these results confirm for the first time the suggestion by Mennella et al. (1996) that irradiated HAC materials might be considered the carrier of the interstellar UV bump at 4.6 μm −1. However, so far the amount of carbon needed to produce the interstellar 4.6 μm −1 band is higher than that available for interstellar carbon dust grains. So the ideal structure of irradiated HAC materials that would produce a band of sufficient strength is not yet clear for the interstellar dust.

Astronomy & Astrophysics, 2012

Context. Mid-infrared (MIR) bands are characteristic for the short-range and medium-range structu... more Context. Mid-infrared (MIR) bands are characteristic for the short-range and medium-range structure of hydrogenated amorphous carbon (HAC) materials that exist in the interstellar medium (ISM) and are sensitive to processing in the harsh interstellar radiation field. Aims. We study the variability of the MIR features from the spectrum of non-processed to that of UV-processed HAC materials and compare them to spectra of interstellar carbonaceous materials. Methods. Nano-sized HAC materials produced by laser ablation were irradiated by vacuum-UV photons with doses comparable to those relevant for interstellar processing. They were subsequently analyzed by IR spectroscopy. Results. In the MIR range, the spectra of HAC materials show many absorption bands such as the sp 3 aliphatic ≡C-H stretching vibration at 3.03 μm, the sp 3 aliphatic-C-H stretching vibration at 3.4 μm and also the sp 3 aliphatic C-H bending vibration at both 6.85 μm and 7.25 μm. All these are recognizable bands of HAC materials. Other absorption bands such as the sp 2 aromatic =C-H stretching vibration at about 3.3 μm and the sp 2-C=C stretching vibration close to 6.25 μm are observed. The HAC materials also possess bands which represent the aromatic out-of-plane bending at 11.65, 12.46 and 12.9 μm in addition to the aromatic-CC -C in-plane bending at 15.87 μm. With UV irradiation, the mass absorption coefficient of the 3.03 μm band completely disappears and that of the aliphatic C-H bands (3.4, 6.85 and 7.25 μm) decreases. This reduction shows that the UV radiation destroys most of the aliphatic C-H bonds inside the HAC structure. On the other hand, the strength of the aromatic 6.2 μm band increases, which is evidence of the partial graphitization within UV-irradiated HAC materials. Because UV irradiation is not uniform, this band agrees well with the C-class PAH toward HD 100764. The C-H out-of-plane vibration bands are strongly affected by UV irradiation. Bands at 11.35, 12.14 and 12.64 μm (solo, duo and trio, respectively), which are found for PAHs of many interstellar spectra were observed partially and were compared to those of non-processed materials, in particular, those at 11.35 μm, which represent the aromatic structures. Conclusions. UV irradiation has a variable effect on both aliphatic and aromatic bands in the MIR region. The aliphatic C-H structure decreases while the aromatic C=C structure, which might lead to the graphitic colonies for PAHs, increases. UV irradiation has revealed solo, duo and trio bands that are relatively consistent with those of the A-and B-class PAHs.

Astronomy & Astrophysics, 2013

Context. Aromatic =CH and C=C vibrational bands have been observed within shocked interstellar re... more Context. Aromatic =CH and C=C vibrational bands have been observed within shocked interstellar regions, indicating the presence of aromatic emission carriers such as PAHs, which may have been created from adjacent molecular cloud material by interaction with a shock front. Aims. We investigate the evolution of the aromatic =CH and C=C vibrational modes at 3.3 and 6.2 μm wavelength in heated HAC materials, PAHs and mixed PAHs and HACs, respectively, aiming at an explanation of the evolution of carbonaceous dust grains in the shocked regions. Methods. Materials used in these analogs (HAC and PAH materials) were prepared by the laser ablation and the laser pyrolysis methods, respectively. The transmission electron microscopy (TEM) in high-resolution mode was used as an analytical technique to characterize the aromatic layers in HACs. Spectroscopic analysis was prformed in the mid-IR range. Results. A remarkable destruction of aliphatic structures in HACs has been observed with the thermal processing, while aromatic structures become dominating by increasing the diameters of the graphene layers. The aromatic bands at 3.3 and 6.2 μm, observed in the laboratory spectra of PAHs and of the combination of the PAHs and HAC materials, are also clearly observed in the spectrum of the heated HACs. These bands agree with those of aromatic bands observed in astronomical observations. Conclusions. Aromatization of HACs could be a pre-stage in the decomposition process of hydrocarbons that form PAH-clusters in such hot interstellar medium.

EAS Publications Series, 2012

Hydrogenated amorphous carbons (HACs) are considered as laboratory analogues to cosmic carbonaceo... more Hydrogenated amorphous carbons (HACs) are considered as laboratory analogues to cosmic carbonaceous nanoparticles in the interstellar medium (ISM). The optical properties of nano-sized HACs may be influenced by the UV processing. The variation of the internal structure leads to dramatic changes in the spectral properties in the FUV-VIS range. This scenario can explain some astronomical features such as the interstellar UV bump at 4.6 µm −1. The spectrum of HACs, irradiated by a dose of UV irradiation that corresponds to 21-33% of the average dose of the UV radiation in diffuse ISM, exhibits a new band centered at 4.6 µm −1. This result confirms, for the first time, the suggestion by Mennella et al. (1996) that irradiated HACs might be considered as the carriers of the interstellar UV bump at 4.6 µm −1. However, the amount of carbon needed to reproduce this band is higher than that available for interstellar carbon dust grains. So the ideal structure of irradiated HACs that would produce a band of sufficient strength has still to be searched for.

Physical Science International Journal, 2015