Comparison between the British and American Methods in Designing Concrete using Local Aggregate in the City of Mosul Preparation

This research included an applied study for the design of concrete mixtures by following the method of the American Concrete Institute (ACl) and the method of the Building Research Center in England (British method) to restriction which of these two methods is more suitable for use and application in the design of concrete mixtures when using local aggregate (gravel and sand taken from the area Badush and Aski Mosul), where job mixes were made using the mixing ratios obtained from these two methods, and a comparative study was made for the properties concrete resulting in the soft state (workability )and the hardened state (compressive resistance), and the results proved the following: A- In general, when discussing the results according to mixing ratios and workability levels, the method of the Building Research Center in England (the British method) gave higher results than the results obtained by the American Concrete Institute method (the American method) when using the above local aggregate whereas results shown increase in (workability) and Compressive strength. This increase amounts to the percentages shown in the table below: Compressive strength (%) Slump test (%) workability 10.48 14.40 Precipitation = 10-8 cm 12.10 21.40 Precipitation = 18-15 cm Table (1-1) B- It is possible to make another comparison, when fixing the proportion of water/cement, it turns out that the method of the Building Research Center in England (the British method) gives higher workability than the method of the American Concrete Institute (the American method) and for the same proportion of cement/ water, the American method gives Higher compressive strength than the British method. C- The building research center method is a more practical and applicable method more than the American Concrete Institute method because it takes the type of cement, the type of aggregate and other properties of the aggregate (especially particle shape) into consideration

NuSTAR monitoring of MAXI J1348-630: evidence of high density disc reflection

We present the broadband spectral analysis of all the six hard, intermediate and soft state NuSTAR observations of the recently discovered transient black hole X-ray binary MAXI J1348-630 during its first outburst in 2019. We first model the data with a combination of a multi-colour disc and a relativistic blurred reflection, and, whenever needed, a distant reflection. We find that this simple model scheme is inadequate in explaining the spectra, resulting in a very high iron abundance. We, therefore, explore the possibility of reflection from a high-density disc. We use two different sets of models to describe the high-density disc reflection: relxill-based reflection models, and reflionx-based ones. The reflionx-based high-density disc reflection models bring down the iron abundance to around the solar value, while the density is found to be $10^{20.3-21.4} \rm cm^{-3}$. We also find evidence of a high-velocity outflow in the form of ∼7.3 keV absorption lines. The consistency between the best-fit parameters for different epochs and the statistical significance of the corresponding model indicates the existence of high-density disc reflection in MAXI J1348-630.

NuSTAR and Swift Observations of the Extragalactic Black Hole X-ray Binaries

We present the results obtained from detailed spectral and timing studies of extra-galactic black hole X-ray binaries LMC X–1 and LMC X–3, using simultaneous observations with Nuclear Spectroscopic Telescope Array (NuSTAR) and Neil Gehrels Swift observatories. The combined spectra in the 0.5 − 30 keV energy range, obtained between 2014 and 2019, are investigated for both sources. We do not find any noticeable variability in 0.5 − 30 keV light curves, with 0.1 − 10 Hz fractional rms estimated to be <2 per cent. No evidence of quasi-periodic oscillations is found in the power density spectra. The sources are found to be in the high soft state during the observations with disc temperature Tin ∼ 1 keV, photon index, Γ > 2.5 and thermal emission fraction, fdisc > 80 per cent. An Fe Kα emission line is detected in the spectra of LMC X–1, though no such feature is observed in the spectra of LMC X–3. From the spectral modelling, the spins of the black holes in LMC X–1 and LMC X–3 are estimated to be in the range of 0.92 − 0.95 and 0.19 − 0.29, respectively. The accretion efficiency is found to be, η ∼ 0.13 and η ∼ 0.04 for LMC X–1 and LMC X–3, respectively.

Effect of Sulfate Crystallization on Sandstone in the Yungang Grottoes

Subjected to various weathering in nature over long time, sandstone has been deteriorated in the Yungang Grottoes. The repeated dissolution and crystallization of soluble salts are important factors that cause the deterioration of the grotto sandstone. In order to study the action mechanism of sulfate crystallization in the Yungang Grottoes sandstone, deterioration tests were carried out by the “soaking-evaporation” cycle of saturated magnesium sulfate (MgSO4) and saturated sodium sulfate (Na2SO4) solutions in laboratory. The test results show that the participation of sulfate greatly accelerated the weathering speed of sandstone. The ultrasonic velocity of the specimens circulated in both Na2SO4 and MgSO4 solutions show a trend of first increasing and then decreasing, and changes more obviously in Na2SO4 solution. In the evaporation stage of the circulation, the peeling mass of the specimens circulated in Na2SO4 solution is significantly greater than that in MgSO4 solution. From the evaporation tests on saturated Na2SO4 and MgSO4 solutions and observation with optical microscope and scanning electron microscope, it is found that a dense crystal layer was formed on the surface during the evaporation of saturated MgSO4 solution, and it gradually seals the internal solution, slowing down the further evaporation. During the solution evaporation, Na2SO4 crystallizes into powdery crystals in a flocculent and soft state, and there are pores between the crystal grains. The change in the ultrasonic velocity of specimens in the "soaking-evaporation" cycle tests can be explained by the evaporation test results.

A maximum X-ray luminosity scale of disc-dominated tidal destruction events

We develop a model describing the dynamical and observed properties of disc-dominated TDEs around black holes with the lowest masses (M ≲ few × 106M⊙). TDEs around black holes with the lowest masses are most likely to reach super-Eddington luminosities at early times in their evolution. By assuming that the amount of stellar debris which can form into a compact accretion disc is set dynamically by the Eddington luminosity, we make a number of interesting and testable predictions about the observed properties of bright soft-state X-ray TDEs and optically bright, X-ray dim TDEs. We argue that TDEs around black holes of the lowest masses will expel the vast majority of their gravitationally bound debris into a radiatively driven outflow. A large-mass outflow will obscure the innermost X-ray producing regions, leading to a population of low black hole mass TDEs which are only observed at optical & UV energies. TDE discs evolving with bolometric luminosities comparable to their Eddington luminosity will have near constant (i.e. black hole mass independent) X-ray luminosities, of order LX, max ≡ LM ∼ 1043 − 1044 erg/s. The range of luminosity values stems primarily from the range of allowed black hole spins. A similar X-ray luminosity limit exists for X-ray TDEs in the hard (Compton scattering dominated) state, and we therefore predict that the X-ray luminosity of the brightest X-ray TDEs will be at the scale LM(a) ∼ 1043 − 1044 erg/s, independent of black hole mass and accretion state. These predictions are in strong agreement with the properties of the existing population (∼40 sources) of observed TDEs.

Broadband ‘spectro-temporal’ features of extragalactic black hole binaries LMC X-1 and LMC X-3: An AstroSat perspective

We present the first results of extragalactic black hole X-ray binaries LMC X-1 and LMC X-3 using all the archival and legacy observations by AstroSat during the period of 2016 − 2020. Broadband energy spectra (0.5 − 20 keV) of both sources obtained from the SXT and LAXPC on-board AstroSat are characterized by strong thermal disc blackbody component (kTin ∼ 1keV, $f_{disc}>79\%$) along with a steep power-law (Γ ∼ 2.4 − 3.2). Bolometric luminosity of LMC X-1 varies from $7-10\%$ of Eddington luminosity (LEdd) and for LMC X-3 is in the range $7-13\%$ of LEdd. We study the long-term variation of light curve using MAXI data and find the fractional variance to be $\sim 25\%$ for LMC X-1 and $\sim 53\%$ for LMC X-3. We examine the temporal properties of both sources and obtain fractional rms variability of PDS in the frequency range 0.002 − 10 Hz to be $\sim 9\%-17\%$ for LMC X-1, and $\sim 7\%-11\%$ for LMC X-3. The ‘spectro-temporal’ properties indicate both sources are in thermally dominated soft state. By modelling the spectra with relativistic accretion disc model, we determine the mass of LMC X-1 and LMC X-3 in the range 7.64 − 10.00 M⊙ and 5.35 − 6.22 M⊙ respectively. We also constrain the spin of LMC X-1 to be in the range 0.82 − 0.92 and that of LMC X-3 in 0.22 − 0.41 with 90% confidence. We discuss the implications of our results in the context of accretion dynamics around the black hole binaries and compare it with the previous findings of both sources.

The study of multipeaked type-I X-ray bursts in the neutron star low-mass X-ray binary 4U 1636 − 536 with RXTE

ABSTRACT We have found and analysed 16 multipeaked type-I bursts from the neutron-star low-mass X-ray binary 4U 1636 − 53 with the Rossi X-ray Timing Explorer (RXTE). One of the bursts is a rare quadruple-peaked burst that was not previously reported. All 16 bursts show a multipeaked structure not only in the X-ray light curves but also in the bolometric light curves. Most of the multipeaked bursts appear in observations during the transition from the hard to the soft state in the colour–colour diagram. We find an anticorrelation between the second peak flux and the separation time between two peaks. We also find that in the double-peaked bursts the peak-flux ratio and the temperature of the thermal component in the pre-burst spectra are correlated. This indicates that the double-peaked structure in the light curve of the bursts may be affected by enhanced accretion rate in the disc, or increased temperature of the neutron star.