Recent advances in polymer layered silicate nanocomposites especially improve flammability resistance; encourage the examination of this unique class of evolving materials as potential ablatives. ...Polymer layered silicate nanocomposites show excellent potential as ablative heat shields. Determining the thermal diffusivity together with the mass and energy transfer is an important problem encountered in design of heat shield system which pyrolyses and ablates at high temperature. The aim of this work is to give information on the influence of the experimental conditions to the estimated effective thermal diffusivity of ablative nanocomposite and composite materials. Here, we present the inverse solution to estimate the parameter used to identify the effective thermal diffusivity of resol type phenolic resin-asbestos cloth montmorillonite layered silicate nanocomposite and its composite counterpart. The experimental setup consists of a standard oxyacetylene flame test. The transient temperature measurements, taken from the top surface and through the thickness of the samples, are used in the inverse analysis to estimate the change of the effective thermal diffusivity. The results of this work clarify the mechanism of the ablation and thermal diffusivity of the layered silicate nanocomposite heat shields due to the high temperature degradation in comparison with its composite counterpart.
Interfacial tension values of two liquid–liquid–vapour systems, a ternary water–decane–methane and a quaternary water–cyclohexane–decane–methane, were measured using a pendant drop technique at 150
...°C and high pressures up to 28.1
MPa. The tested ternary mixture showed a maximum liquid–liquid interfacial tension by increasing pressure whereas it only slightly increased liquid–liquid interfacial tension in the quaternary system. The predicted interfacial tension values by some models are compared and the application of liquid–liquid interfacial tension models for predicting the liquid–vapour interfacial tension at high pressure conditions is discussed.
It is shown that the liquid–liquid interfacial tension in binary and ternary aqueous–hydrocarbon systems at any temperature can be determined by knowing the molar compositions of the bulk fluid ...phases and a system-dependent constant. The system-dependent constant has been found to be related to saturation adsorption. Based on these findings, a new equation has been proposed for reliable prediction of interfacial tension in aqueous–organic systems. The model is simple to use and reasonably describes the interfacial tension of binary water–hydrocarbon mixtures and some ternary aqueous–organic systems. The new equation shows an apparent inconsistency near the critical point which is explained using the underlying mono-molecular layer assumption.
Abstract Black hole (BH) X-ray binaries (XRBs) are ideal targets to study the connection between accretion inflow and jet outflow. Here we present quasi-simultaneous, multiwavelength observations of ...the Galactic BH system MAXI J1820+070, throughout its 2018–2019 outburst. Our data set includes coverage from the radio through X-ray bands from 17 different instruments/telescopes, and encompasses 19 epochs over a 7 month period, resulting in one of the most well-sampled multiwavelength data sets of a BH XRB outburst to date. With our data, we compile and model the broadband spectra of this source using a phenomenological model that includes emission from the jet, a companion star, and an accretion flow. This modeling allows us to track the evolution of the spectral break in the jet spectrum, a key observable that samples the jet launching region. We find that the spectral break location changes over at least ≈3 orders of magnitude in electromagnetic frequency over this period. Using these spectral break measurements, we link the full cycle of jet behavior, including the rising, quenching, and reignition, to the changing accretion flow properties as the source evolves through its different accretion states. Our analysis shows consistent jet behavior with other sources in similar phases of their outbursts, reinforcing the idea that jet quenching and recovery may be a global feature of BH XRB systems in outburst. Our results also provide valuable evidence supporting a close connection between the geometry of the inner accretion flow and the base of the jet.
A large number of studies showed that nanoparticles used even in small quantities improve thermal stability and flammability resistance by reducing significantly the mass loss and heat release rate. ...Recently, a graphite nano-crystal and nano-clay have been used as an alternative to traditional fire retardants to improve the thermal stability and flammability resistance of polymeric materials.
The objectives of this work are the experimental and theoretical evaluation of the pyrolysis and flammability of the polymer nanocomposites based on novolac type phenolic resin and graphite nano-crystal under the external convection and radiation heat flux. The theoretical results of heat release rate modeling based on conservation equations of mass and energy are then confirmed by the experimental data of thermal analysis.
Nano-graphite shows good potential as flame retardant because upon pyrolysis of polymer, the nano-crystal graphite reinforced phenolic resin can be converted into a uniform carbon layer, which may lead to significantly higher resistance to oxidation compared to neat phenolic resin. Formation of this carbon layer on char formed from the pyrolysis of the nanocomposite at high temperature not only enhances the char mechanical strength, but also acts as secondary protection layer to protect the lower remained nanocomposite.
•We examine the thermal and flammability analysis of novolac/graphite nanocomposites at different testes.•We analyse different alternatives for determination of the thermal performance of nanocomposites.•Thermal degradation behavior of nanocomposites were modeled and explained.
Lichen planus is a chronic inflammatory immunologic-based disease involving skin and mucosa. This disease is generally divided into two categories: erosive and non-erosive. Many etiologic factors are ...deliberated regarding the disease; however, the disorders of immune system and the role of cytotoxic T-lymphocytes and monocytes are more highlighted. Zinc is an imperative element for the growth of epithelium and its deficiency induces the cytotoxic activity of T-helper2 cells, which seems to be associated with lichen planus.
This study was aimed to evaluate the levels of serum zinc in erosive and non-erosive oral lichen planus (OLP) and to compare it with the healthy control group to find out any feasible inference.
A total of 22 patients with erosive oral lichen planus, 22 patients with non erosive OLP and 44 healthy individuals as the control group were recruited in this descriptive-comparative study. All the participants were selected from the referees to the department of oral medicine, school of dentistry, Tabriz University of Medical Sciences. Serum zinc level was examined for all the individuals with liquid-stat kit (Beckman Instruments Inc.; Carlsbad, CA). Data were analyzed by adopting the ANOVA and Tukey tests, using SPSS 16 statistical software.
The mean age of patients with erosive and non-erosive LP was 41.7 and 41.3 years, respectively. The mean age of the healthy control group was 34.4 years .The mean serum zinc levels in the erosive and non erosive lichen planus groups and control groups were 8.3 (1.15), 11.15 (0.92) and 15.74 (1.75) μg/dl respectively. The difference was statistically significant (p< 0.05).
The serum zinc levels were decreased in patients with erosive oral lichen planus. This finding may probably indicate the promising role of zinc in development of oral lichen planus.
Oral lichen planus (OLP) is a chronic inflammatory oral mucosal disease with indefinite etiology. In recent researches, free radicals have been deliberated as the possible etiology of inflammatory ...and autoimmune diseases.
This study was aimed to evaluate the stress oxidative status with the nitric oxide (NO) index in a sample of Iranian population.
In this descriptive-comparative study, serum NO level was assessed in 20 OLP patients as the case group and 20 healthy individuals as the control group. Collected data were analyzed by adopting two Sample t-test, using SPSS 16 software. The statistical significance level was set at p< 0.05.
The mean serum NO levels in OLP patients and healthy controls were 17.1±3.4 ng/ml and 14.5±2.7 ng/ml respectively; which revealed a significant statistical difference (p= 0.009).
The results of the current study with its limitation may support the premise that higher serum levels of NO in patients with OLP might activate the process of lymphocytes and cellular immunity system; hence, possibly endorsing the effect of serum NO in pathogenesis of lichen planus.
Monitoring the cooling of neutron-star crusts heated during accretion outbursts allows us to infer the physics of the dense matter present in the crust. We examine the crust cooling evolution of the ...low-mass X-ray binary MXB 1659−29 up to ∼505 days after the end of its 2015 outburst (hereafter outburst II) and compare it with what we observed after its previous 1999 outburst (hereafter outburst I) using data obtained from the Swift, XMM-Newton, and Chandra observatories. The observed effective surface temperature of the neutron star in MXB 1659 − 29 dropped from ∼92 eV to ∼56 eV from ∼12 days to ∼505 days after the end of outburst II. The most recently performed observation after outburst II suggests that the crust is close to returning to thermal equilibrium with the core. We model the crust heating and cooling for both its outbursts collectively to understand the effect of parameters that may change for every outburst (e.g. the average accretion rate, the length of outburst, the envelope composition of the neutron star at the end of the outburst) and those which can be assumed to be the same during these two outbursts (e.g. the neutron star mass, its radius). Our modelling indicates that all parameters were consistent between the two outbursts with no need for any significant changes. In particular, the strength and the depth of the shallow heating mechanism at work (in the crust) were inferred to be consistent during both outbursts, contrary to what has been found when modelling the cooling curves after multiple outburst of another source, MAXI J0556−332. This difference in source behaviour is not understood. We discuss our results in the context of our current understanding of cooling of accretion-heated neutron-star crusts, and in particular with respect to the unexplained shallow heating mechanism.
The black hole transient GRS 1915+105 entered a new phase of activity in 2018, generally characterised by low X-ray and radio fluxes. This phase has only been interrupted by episodes of strong and ...variable radio emission, where high levels of X-ray absorption local to the source were measured. We present 18 epochs of near-infrared spectroscopy (2018–2023) obtained with GTC/EMIR and VLT/X-shooter, spanning both radio-loud and radio-quiet periods. We demonstrate that radio-loud phases are characterised by strong P-Cygni line profiles, indicative of accretion disc winds with velocities of up to ∼3000 km s
−1
. This velocity is consistent with those measured in other black hole transients. It is also comparable to the velocity of the X-ray winds detected during the peak outburst phases in GRS 1915+105, reinforcing the idea that massive, multi-phase outflows are characteristic features of the largest and most powerful black hole accretion discs. Conversely, the evolution of the Br
γ
line profile during the radio-quiet phases follows the expected trend for accretion disc lines in a system that is gradually decreasing its intrinsic luminosity, exhibiting weaker intensities and more pronounced double-peaks.
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